Hi, Andy. sorry for disappearance - my win7 died, and outdated comm programs doesn't seem to work with latest version. Can be fixed by recompiling client/server or game exe, but don't really have time to configure all that from scratch. But I can propose some code analyzes instead.

Most related ingame code stored in "sharedmem.c" file. Here script create object "shared_memory_t" type with "EECHSharedMemory" name (it is important) that will be used as data container for lamps states, upfront display, basic dynamics - pitch roll engines data etc. Full list in update_dynamics_shared_mem() function, also waypoints and weapons. Problem in any of the function can stop process, so it's worth to check debug version in case some asserts triggered (or at least enabled debug logging option in eech.ini).

Shared memory initialization happen on game load, single message should appear:
Initialising Shared Memory

And another one can appear after it if something wrong:
Failed to initialise shared memory


Last changes in this file:

by javelin 20.07.2019 (Commserver Fix, Joystick Deadbands Fix, Havoc Engine Gauges Added)
Two new variables was added - num_flares and num_chaff. looks safe, even if these values can be extracted from weapons data array (I guess, maybe not). Version was changed from 3 to 4 (so only latest version of commserver/client can be used - i.e. compiled after value was changed).

by messyhead 27.03.2020 (Updating ekran display)
ka50 ekran data added, looks ok. version was not changed.


And now how EECHCommUDPServer.exe reading and sending shared data.

Program using CreateFileMapping function to load shared file "EECHSharedMemory", parse it data and send to the client by TCP or UDP (not sure how it chose which one is required).
To debug network exchange, you can add debugLevel value to the application args, like:

> EECHCommUDPServer 1234 1

so you will see in the console what is going on between client and server.

So first thing to check that your server/client EXEs was compiled after 20.07.2019 so they have new version number. or even maybe after 27.03.2020 as server uses same variables list? not sure but it may be an issue you experiencing.
Maybe some programs exists that can load shared memory file by name so you will see that game pushing some data.
Hope this information helps somehow. If not, I may try to make compilers work and test whole process some day.