Basically, I've only seen this issue in the nether so this may just be in the nether. But basically say I've placed a bed to go find netherite, because of the explosion fire goes everywhere which is expected however if I break the block underneath the fire without destroying the fire first, even though the fire isn't visible when you walk into the block you start to take fire damage.

Attached in this report is a video of the bug, I've tested this around 7 times before recording. This issue I do know also occurred in 1.16.0+ however I don't know about 1.17.20.20 beta.