When you apply yourself Regeneration level 255 (max you can in mc java) and stand in lava, the lava won't kill you; UNLESS you re-log. Once you re-log, standing in lava with regeneration 255, the lava won't hurt you for the first few seconds, then start killing you even though it shouldn't be able to. (I can't fit the video because the video size limits to 10MB, max I can compress it to is 12MB)
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Avoma
This appears to be a duplicate of MC-21650, which hasn't yet been resolved. If you have any additional information to provide regarding this issue, feel free to comment on the parent ticket. If you feel that this issue is affecting you, feel free to vote for the duplicated ticket, to give Mojang a basic idea of how many people are impacted by the problem. Just to further inform you, this will not determine how quickly the bug gets handled or fixed.