diff --git a/coordinator/coordinator.lua b/coordinator/coordinator.lua
index aa29ee8..80c21b6 100644
--- a/coordinator/coordinator.lua
+++ b/coordinator/coordinator.lua
@@ -54,9 +54,9 @@ end
 function coordinator.configure_monitors(num_units, disable_flow_view)
     ---@class monitors_struct
     local monitors = {
-        primary = nil,
+        primary = nil,      ---@type table|nil
         primary_name = "",
-        flow = nil,
+        flow = nil,         ---@type table|nil
         flow_name = "",
         unit_displays = {},
         unit_name_map = {}
diff --git a/coordinator/startup.lua b/coordinator/startup.lua
index 6363727..c5db484 100644
--- a/coordinator/startup.lua
+++ b/coordinator/startup.lua
@@ -22,7 +22,7 @@ local sounder     = require("coordinator.sounder")
 
 local apisessions = require("coordinator.session.apisessions")
 
-local COORDINATOR_VERSION = "v1.0.10"
+local COORDINATOR_VERSION = "v1.0.11"
 
 local println = util.println
 local println_ts = util.println_ts
diff --git a/lockbox/digest/md5.lua b/lockbox/digest/md5.lua
index 6ce1df2..b6ff36c 100644
--- a/lockbox/digest/md5.lua
+++ b/lockbox/digest/md5.lua
@@ -1,5 +1,3 @@
-require("lockbox").insecure();
-
 local Bit = require("lockbox.util.bit");
 local String = require("string");
 local Math = require("math");
diff --git a/lockbox/digest/sha1.lua b/lockbox/digest/sha1.lua
index fc38866..3b13937 100644
--- a/lockbox/digest/sha1.lua
+++ b/lockbox/digest/sha1.lua
@@ -1,5 +1,3 @@
-require("lockbox").insecure();
-
 local Bit = require("lockbox.util.bit");
 local String = require("string");
 local Math = require("math");
diff --git a/lockbox/init.lua b/lockbox/init.lua
index caee6c0..698c98e 100644
--- a/lockbox/init.lua
+++ b/lockbox/init.lua
@@ -1,25 +1,6 @@
-local Lockbox = {};
+local Lockbox = {}
 
 -- cc-mek-scada lockbox version
-Lockbox.version = "1.0"
+Lockbox.version = "1.1"
 
---[[
-package.path =  "./?.lua;"
-                .. "./cipher/?.lua;"
-                .. "./digest/?.lua;"
-                .. "./kdf/?.lua;"
-                .. "./mac/?.lua;"
-                .. "./padding/?.lua;"
-                .. "./test/?.lua;"
-                .. "./util/?.lua;"
-                .. package.path;
---]]
-Lockbox.ALLOW_INSECURE = true;
-
-Lockbox.insecure = function()
-    assert(Lockbox.ALLOW_INSECURE,
-            "This module is insecure!  It should not be used in production." ..
-            "If you really want to use it, set Lockbox.ALLOW_INSECURE to true before importing it");
-end
-
-return Lockbox;
+return Lockbox
diff --git a/lockbox/mac/hmac.lua b/lockbox/mac/hmac.lua
index a10b84c..1a02b00 100644
--- a/lockbox/mac/hmac.lua
+++ b/lockbox/mac/hmac.lua
@@ -8,7 +8,7 @@ local HMAC = function()
 
     local public = {};
     local blockSize = 64;
-    local Digest = nil;
+    local Digest;
     local outerPadding = {};
     local innerPadding = {}
     local digest;
diff --git a/lockbox/util/array.lua b/lockbox/util/array.lua
index bd9ed56..b018a7b 100644
--- a/lockbox/util/array.lua
+++ b/lockbox/util/array.lua
@@ -1,4 +1,3 @@
-
 local String = require("string");
 local Bit = require("lockbox.util.bit");
 local Queue = require("lockbox.util.queue");
diff --git a/rtu/modbus.lua b/rtu/modbus.lua
index 06c1273..44900a0 100644
--- a/rtu/modbus.lua
+++ b/rtu/modbus.lua
@@ -215,7 +215,7 @@ function modbus.new(rtu_dev, use_parallel_read)
     ---@param value any
     ---@return boolean ok, MODBUS_EXCODE
     local function _5_write_single_coil(c_addr, value)
-        local response = nil
+        local response = MODBUS_EXCODE.OK
         local _, coils, _, _ = rtu_dev.io_count()
         local return_ok = c_addr <= coils
 
@@ -239,7 +239,7 @@ function modbus.new(rtu_dev, use_parallel_read)
     ---@param value any
     ---@return boolean ok, MODBUS_EXCODE
     local function _6_write_single_holding_register(hr_addr, value)
-        local response = nil
+        local response = MODBUS_EXCODE.OK
         local _, _, _, hold_regs = rtu_dev.io_count()
         local return_ok = hr_addr <= hold_regs
 
@@ -263,7 +263,7 @@ function modbus.new(rtu_dev, use_parallel_read)
     ---@param values any
     ---@return boolean ok, MODBUS_EXCODE
     local function _15_write_multiple_coils(c_addr_start, values)
-        local response = nil
+        local response = MODBUS_EXCODE.OK
         local _, coils, _, _ = rtu_dev.io_count()
         local count = #values
         local return_ok = ((c_addr_start + count) <= (coils + 1)) and (count > 0)
@@ -292,7 +292,7 @@ function modbus.new(rtu_dev, use_parallel_read)
     ---@param values any
     ---@return boolean ok, MODBUS_EXCODE
     local function _16_write_multiple_holding_registers(hr_addr_start, values)
-        local response = nil
+        local response = MODBUS_EXCODE.OK
         local _, _, _, hold_regs = rtu_dev.io_count()
         local count = #values
         local return_ok = ((hr_addr_start + count) <= (hold_regs + 1)) and (count > 0)
@@ -403,7 +403,7 @@ function modbus.new(rtu_dev, use_parallel_read)
         end
 
         if type(response) == "table" then
-        elseif type(response) == "nil" then
+        elseif response == MODBUS_EXCODE.OK then
             response = {}
         else
             response = { response }
diff --git a/rtu/startup.lua b/rtu/startup.lua
index 4bc3868..00c6406 100644
--- a/rtu/startup.lua
+++ b/rtu/startup.lua
@@ -31,7 +31,7 @@ local sna_rtu      = require("rtu.dev.sna_rtu")
 local sps_rtu      = require("rtu.dev.sps_rtu")
 local turbinev_rtu = require("rtu.dev.turbinev_rtu")
 
-local RTU_VERSION = "v1.6.3"
+local RTU_VERSION = "v1.6.4"
 
 local RTU_UNIT_TYPE = types.RTU_UNIT_TYPE
 local RTU_UNIT_HW_STATE = databus.RTU_UNIT_HW_STATE
diff --git a/scada-common/log.lua b/scada-common/log.lua
index 2c266bb..eadc763 100644
--- a/scada-common/log.lua
+++ b/scada-common/log.lua
@@ -16,7 +16,7 @@ local logger = {
     path = "/log.txt",
     mode = MODE.APPEND,
     debug = false,
-    file = nil,
+    file = nil,         ---@type table|nil
     dmesg_out = nil,
     dmesg_restore_coord = { 1, 1 },
     dmesg_scroll_count = 0
diff --git a/scada-common/types.lua b/scada-common/types.lua
index 91e6469..a78b5a2 100644
--- a/scada-common/types.lua
+++ b/scada-common/types.lua
@@ -375,6 +375,7 @@ types.MODBUS_FCODE = {
 -- MODBUS exception codes
 ---@enum MODBUS_EXCODE
 types.MODBUS_EXCODE = {
+    OK = 0x00,
     ILLEGAL_FUNCTION = 0x01,
     ILLEGAL_DATA_ADDR = 0x02,
     ILLEGAL_DATA_VALUE = 0x03,
diff --git a/scada-common/util.lua b/scada-common/util.lua
index a9a9f5b..144f88d 100644
--- a/scada-common/util.lua
+++ b/scada-common/util.lua
@@ -8,7 +8,7 @@ local cc_strings = require("cc.strings")
 local util = {}
 
 -- scada-common version
-util.version = "1.1.0"
+util.version = "1.1.1"
 
 -- ENVIRONMENT CONSTANTS --
 
diff --git a/supervisor/session/rtu/txnctrl.lua b/supervisor/session/rtu/txnctrl.lua
index 9766bab..25ab3ed 100644
--- a/supervisor/session/rtu/txnctrl.lua
+++ b/supervisor/session/rtu/txnctrl.lua
@@ -55,7 +55,7 @@ function txnctrl.new()
     -- mark a transaction as resolved to get its transaction type
     ---@nodiscard
     ---@param txn_id integer
-    ---@return integer txn_type
+    ---@return integer|nil txn_type
     function public.resolve(txn_id)
         local txn_type = nil
 
diff --git a/supervisor/session/rtu/unit_session.lua b/supervisor/session/rtu/unit_session.lua
index 711fc75..3d27fa4 100644
--- a/supervisor/session/rtu/unit_session.lua
+++ b/supervisor/session/rtu/unit_session.lua
@@ -73,7 +73,13 @@ function unit_session.new(session_id, unit_id, advert, out_queue, log_tag, txn_t
         if m_pkt.scada_frame.protocol() == PROTOCOL.MODBUS_TCP then
             if m_pkt.unit_id == unit_id then
                 local txn_type = self.transaction_controller.resolve(m_pkt.txn_id)
-                local txn_tag = " (" .. util.strval(txn_tags[txn_type]) ..  ")"
+                local txn_tag = util.c(" (", txn_tags[txn_type], ")")
+
+                if txn_type == nil then
+                    -- couldn't find this transaction
+                    log.debug(log_tag .. "MODBUS: expired or spurious transaction reply (txn_id " .. m_pkt.txn_id .. ")")
+                    return false, m_pkt.txn_id
+                end
 
                 if bit.band(m_pkt.func_code, MODBUS_FCODE.ERROR_FLAG) ~= 0 then
                     -- transaction incomplete or failed
diff --git a/supervisor/startup.lua b/supervisor/startup.lua
index 3f0d966..a09e058 100644
--- a/supervisor/startup.lua
+++ b/supervisor/startup.lua
@@ -21,7 +21,7 @@ local supervisor = require("supervisor.supervisor")
 
 local svsessions = require("supervisor.session.svsessions")
 
-local SUPERVISOR_VERSION = "v1.0.3"
+local SUPERVISOR_VERSION = "v1.0.4"
 
 local println = util.println
 local println_ts = util.println_ts