So I was driving my boat through the woods, just your average day.
However my quick testing got interrupted by these sudden lag spikes whenever the boat gets near an object.
And by 'near' I don't even mean touching, the boat is a decent amount of distance away from any object, and yet lag.

Also I found that the lag mainly happens when the ground is tilted.
Any idea how to fix this issue?

Are you using convex object?
Their performance is ridiculously low when colliding with characterbody3d.

    Okay, fixed it.
    Turns out having a ConcavePolygonShape3D collision as child of the characterbody caused the issue.
    However putting it under a static body under the characterbody made it work as I want.

    MagickPanda
    No, the issue was caused by a concavepolygon.

      [unknown]
      hmm good to know it's fixed, my issue was 4 character3d with convex shape colliding made the game run at 1 fps -.-