When I activate my machine (pistons), my game sometimes crash, sometimes my hand disapear and sometimes this: (See picture)
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Sure!
[media][media]
[media]
(Cauldron swapper machine)
Thank you for your report!
However, this issue has been closed as a Duplicate of MCPE-33072.
Your additional information and observations are very useful, so if you can add them to the comments section of the parent issue it would be appreciated.
If you have not, you might like to make use of the search feature before making a new ticket, as it's likely that the issue has been reported already.
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Could you please show us the exact setup of your machine?