Pistons can use slime to push them selves causing an issue.

Building a structure like so...
S is a slime block. P is a piston or sticky piston.
sss
sps

Activeating the piston causes a crash.
Note This is a slight variation of the report due to many variations being marked as duplicates and rhe duplicates not being fixed but the orignal being fixed. I will add more of the slight variations to the ticket.

gatharian added:
Additional video provided by MCPE-14860
https://youtu.be/gqb_Hx1X3K8