Helicopter is laggy/choppy recently

I'm having an issue with the helicopter appearing laggy/choppy:

Animals, players, planes are moving normally. Only the helicopter is choppy while the server fps and cpu usage is normal.
With fps.limit = 1000, the server fps is stable at 1000 without any drops, so it's seems not to be related to this?

I tried to unload all plugins, exactly as choppy. No change.

When I launch a fresh server simultaneously on the same CPU as the other with all the plugins, the helicopter moves smooth without any stuttering.