Forge server 16.1.1 (32.0.75) all clients crash?

[Bobb3ll1]

Hey im a part of a minecraft servers development and owner team that just recently is swithing from spigot plugins to forge.
we currently are trying just one mod (ImmersiveEngine) and it worked just fine for a while, but now everyones client crashes with an exit code -1 at the same time.
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The game crashed whilst unexpected error
Error: java.lang.IllegalArgumentException: null
Exit Code: -1

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I can provide crash reports if necessary.
Any help would be appreciated.

Thank you.

[Bobb3ll1]

Heres the debug log. the problem started yesterday and today i tried to get on (around 9:50) it lets me get on for some time and then it crashes.

debug.log

[Bobb3ll1]

Oh sorry here it is.
 

debug.log