While walking around lava lakes, striders can sometimes walk into lava falls, and then rise up all the way to the ceiling, where they get stuck. They don't suffocate or drown and can stay there indefinitely. This often happens in Nether chunks that are loaded for long periods.
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This looks like it duplicates MC-181610
Thank you for your report!
We're tracking this issue in MC-181610, so this ticket is being resolved and linked as a duplicate.
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