When activating 8 sticky pistons with slime blocks and building blocks oriented horizontally the minecraft client crashes back to launcher.
Staggered pistons seems to cause the crash every single time. Other configurations cause crashes as well, but seem less consistent.
Rar of a testing world and the log file have been attached.
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This lists it as a duplicate to a crash that occurs when 64 pistons activate. But the bug report says 63 won't cause a crash.
I have 8 pistons and it crashes.

I can confirm that, when I entered the attached worldsave, I did crash (see attached screenshot) when I activated one of the contraptions' buttons ,but upon re-entering, I could not reproduce that crash anymore. I triggered all buttons of all 3 contraptions which are in that worldsave, but the crash occurred solely when I entered the worldsave first.
Edit: For some reason I am able to crash again (sometimes).
Could any of the mods/helpers maybe download the worldsave and confirm that?
Should we maybe wait until the fix for MC-123304 is in the next snapshot, to see if this still occurs with these few pistons/this setup before you'd reopen the bugpost?
I got it on my to-watch-list and would test it in next snapshot.
I reopened this report because 64 != 8, but then I decided to leave it closed for now. If this still happens in the next snapshot even though the crash described in MC-123304 does not happen anymore, please comment here.

It's the same thing, it's not about the amount of pistons, it's about the amount of piston entities (moving blocks).
Please see this reddit post for further information about this bug.