[1.12.2 Forge] Stuck Between Dimensions

[Flexico]

I'm running a server that a few of my friends are playing on, and almost everything runs fine, except that whenever someone tries to switch dimensions, as soon as the target dimension loads, the game starts teleporting them back, and they get bounced back and forth until the game times out and kicks them from the server. I have no idea what mod(s) could be causing this, so here's my mod list (see screenshot):

And here's my Forge logs:
Server: https://pastebin.com/TuiqFzyx
Client: https://pastebin.com/63Ka2kZi (this one was too big for pastebin, so I just posted the error messages)

 

[grandrolf]

Can you try and move your installation out from your dropbox folder (do a copy/paste - don't actually move the files, if there's dodgy permissions stuck on the files and folders), - there's all kinds of issues that can happen when running the server inside a folder that's synced. (regardless of engine - seen this on Dropbox, OneDrive and others - due to files being locked or similar).

 

[Flexico]

I quit Dropbox to disable the syncing, and tried again and got the same thing. I've been running my Minecraft instances from that folder for about 2 years with no major problems! Even this same server worked much more smoothly before, and I have no idea what changed to make dimension switching so buggy.