Proper Debug of "Mismatched mod Channel List"

Im managing a Minecraft server for the kids.  Ive been running Minecraft servers since the 1.12 days... nothing really hard about it.... (30 year Unix linux admin here - managed dynix through AIX, HPUX, Linux... been doing this awhile...)

Then they discover mods......

so the server is running and all is fine, then they attempt to connect and we get the "Mismatched mod channel list" more than half the time...  sometime a restart of the server fixes it, usually though we shut it down, come back tomorrow restart and all is fine... ?!?!?!?!

- Checked permissions on all the files, but this doesn't really account for sometimes it works sometimes it doesn't.. (no SeLinux running)

- Running the server on console, and not in Service has no affect either way

- Running as root (I know bad idea) or as normal user with proper access has no affect.

- Client are all "regular" Minecraft installs and forge and no difference in the way they login or run the app vs working or not working..

To date all the "solutions" that I see are to do some crazy crap like "copy all the mods from one directory on the client/server to the other" ...  Sorry this isn't a "solution" that's a bunch of crap...  

So how can this be debugged? in looking at the logs I don't see an entry that states "missing X mod" or something useful..  Where are the logs that will help to debug this?  I want to learn more about how this system evaluates and communicated the "mod channel list" so I can see what is happening..

Server is running: Linux 4.15.0-128-generic #131~16.04.1-Ubuntu SMP Wed Dec 9 17:33:47 UTC 2020 x86_64 x86_64 x86_64 GNU/Linux

Client are all Macs:  MC version 1.14.4 / Forge 28.2.0 / mods are XLife modpack

What else you need? 

Thanks... 

Frustrated Father (I'm locked in covid style with a Minecraft group that won't run... god help us all.. ) :-)