Most nether mobs are immune to burning, but they can burn in lava cauldrons. All you need to do to reproduce is to put a mob immune to lava (ex. zombified piglins, blazes, etc.) in a lava cauldron.
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As far as I am aware, this isn't an issue in Java Edition but is in Bedrock Edtion. With that being said, would MCPE-65962 happen to describe your problem?
Could not reproduce. Plus this was already fixed in 1.17.1.