Double tapping an item in the inventory or in a chest doesn't group all the items of the same type into one slot.
How to produce:
Start a new creative world.
Place down a chest.
Pick a stack of a random item from the inventory.
Spread that stack on multiple slots inside the chest.
Double tap one of the slots with the item in it.
You'll notice that instead of having all the items regroup into one slot, nothing happens.
Thank you for your report!
We're actually already tracking this issue at MCPE-66458, so I will resolve and link this ticket as a duplicate.
If you would like to add a vote and any extra information to the main ticket it would be appreciated.
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