If you're crouching while opening a menu/inventory/chest etc, you will be standing upright after exiting said menu and will no longer crouch.
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Comments 2
Thank you for your report!
However, this issue has been closed as a Duplicate of MCPE-33209.
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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Confirmed on Android Nougat LG Q6. Has resulted in death and near death many times. Hope this bug gets patched very soon.