https://www.dropbox.com/s/7bpk9vcbdsq2mup/working-mods.zip?dl=0
This set of mods, with the mod-list.json works. Enable one more and it doesn't.

https://www.dropbox.com/s/1p4z81m558pwioq/cm-mods.zip?dl=0
This is a set of mods which run and work on KatherineOfSky's community server. Note that I am ...

After further diagnosis I have come to the conclusion that it's related to my network setup due to testing a set of mods which are known working on another person's server. Would be grateful for some explanation as to what these messages actually mean (in terms of packets over the network) to help ...

It happens every time, but only when a certain amount of mods are present, which varies depending on the mods. Unfortunately I don't have the logs anymore but I'll try and reproduce.

When I try to connect to a server through the matching server I get the error "Couldn't establish network communication with server."

From client logs:
10123.898 Joining game 80.229.224.55:34197
10123.898 Info UDPSocket.cpp:33: Opening socket
10123.899 Info ClientMultiplayerManager.cpp:539 ...