When a piston pushes a cauldron, it simply cannot and lags out (a.k.a. quitting the game by the system)
Linked issues
duplicates 1
Comments 2
Thank you for your report!
However, this issue has been closed as a Duplicate of MCPE-14805.
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Just a few things to add is that the things you have build in the world may not save. I do not know if that is a bug but it only happens only when this bug happens.