Issue with lag / lerp on multiplayer server (Sandbox) - usermessage related

Hey Help & Support people!

There is this issue on the sandbox server I frequent. It appears that every time there’s some contraptions out, the usermessage count goes completely mad. I took this picture today of the issue.

http://cloud-4.steampowered.com/ugc/593663499558903598/6BF4A01034FE3E661A07928B4A04D552C656FB8F/

Notice the amount of usermessages. There are sometimes so many usermessages that they go outside of the graph. It only happens when there’s a good chunk of contraptions out, but nothing special. Other servers seem to be able to handle more.
Do anyone here know where this issue originates? The server is running the normal build tools (Easy Precision, Precision Allignment, etc) and mobility addons like ACF.

Any help or tips on how to get the performance better are appreciated!

It’ll be a pain in the ass but disabling each addon one by one should yield the answer.

What prop protection are you running?