The most likely cause is image stabilization being left on while the camera was on a tripod. IBIS/lens stabilization can drift during long tripod-mounted sequences, then recenter, which creates the jagged or stepped star trails you’re seeing.

Other possible contributors are slight camera movement (tripod vibration, wind, something touching the setup) and atmospheric turbulence, especially near the ocean where air movement can be stronger.

To prevent it next time:

• Turn off in-body and lens stabilization when shooting star trails on a tripod.
• Make sure the tripod is very stable and protected from wind or accidental bumps.
• Keep using a remote release and avoid touching the camera.
• If possible, choose calmer conditions.

In post, there’s no perfect fix if the frames themselves are misaligned by stabilization drift. You can sometimes improve the result by aligning individual frames before stacking, but if the shift varies within or between exposures, the artifacts may remain. The best solution is to reshoot with stabilization off and a stable setup.