Same exact thing is happening to me. I made a nano farm with a piston yesterday, worked fine. Tried making a kelp farm today, kept crashing when trying to use a piston. Hopper clocks, buttons etc. Nothing worked. Went back to test my nano farm, crashed. I did reinstall the server today though for unrelated reasons. Maybe 25.0.85 is causing the issues.
Edit: Just reinstalled to a previous version I was sure I had yesterday, still crashed. RIP. Here is my log for comparison:
crash-2019-03-16_21.21.13-client.txt