I searched for this but could not find it reported. I tried to select iPhone 8 and 8 Plus because it happens on two different phones, and also on iPad Mini and 4th Gen. Selecting iPhone 8 was not an option on the list.
In my family we call this "Punching Hand Syndrome." When using touch on iOS devices (but NOT when using a Nimbus controller) Steve often get's "stuck" mining. We might harvest a few carrots, but then we get Punching Hand Syndrome and the next thing you know . . . the dirt is punched out and the wall is broken and unless you're pretty quick to point up into the air, it can cause a lot of damage.
We have found that pausing the game reliably stops an episode of PHS.
I don't remember exactly when this started, but it started all of a sudden one day and it was a while back, before the Update Aquatic.
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Thank you for your report!
However, this issue has been closed as a Duplicate of MCPE-30151.
Please add a vote and any new information to the main ticket, which will be updated accordingly.
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This issue is a duplicate of MCPE-30151, which has already been linked as related.