Hello good sirs,
So I had previously looked into this so I can give some insight though obviously I'm not a gmod expert like others.
When we had first moved over ARCCW there was an issue with the lrb_tracer where it wasn't being killed properly.
This had ultimately caused a lua effect loop which made things like NPCs not have tracers etc for client side.
In addition to the above, clients are expected to have Much Lower FPS to someone that has joined the server as it effects are client side.
So re-joining the server will remove these effects.
As a request Synergy and to any other players.
If they get this within console can you please do the following:
Open Console `
Type
FProfiler
Top Left - Start Profiling
Run for 10 seconds
Stop Profiling and then click on "Total Time in MS"
This should indicate what is taking up the most resources on your client.
An example can be shown below where I had identified that the LRB_tracer was not being deleted properly.
This was fixed a while back.
Hopefully this helps in trying to identify this issue.