Afternoon,
I had updated a bunch of mods today and found that when trying to connect to a Waterfall/Paper multiplayer server, it would either disconnect me immediately or within a minute or so of being connected. All it'd say was "Connection Lost" and wouldn't allow me to disconnect. After removing all mods and re-adding one by one, Light Overlay appeared to be the one to make it disconnect. It would throw a "[Netty Epoll Client IO #1/WARN]: Received invalid channel identifier "legacy:fml|hs" from connection net.minecraft.class_2535@5021ecec" in latest.log before disconnecting. See: https://pastebin.com/F9Hzw7XF.
nostrip-1.2.0-1.16.2+, loader 0.11.1-1.16.5, API 0.30.0 (though 0.29.4 didn't work either.)

Appears to be fixed. Not sure which thing fixed it but something did... will keep on the lookout for further issues