Unknown

They despawn

Or burn in lava

My friend was watching them, and there was no lava or fire nearby 

Even if someone's watching them they disappear after 5minutes

So that piece of carpet I left in the nether on the floor for 2 MONTHS is excluded? I returned after 1 minute

Thank you for your report!
We're tracking this issue in MCPE-48370, so this ticket is being resolved and linked as a duplicate.

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