When holding to select a whole stack, only a single item is grabbed.
Linked issues
Comments 2
Thank you for your report!
However, this issue has been closed as a Duplicate of MCPE-30215.
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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I'm having the same problem but on Android