I was using beds to find ancient debris. When I was walking around the hole I blew up to collect the blocks I was randomly set on fire. I wasn't on top of any magma block there wasn't any fire or lava near me and there weren't any mobs near me either. The fire lasted a long time and took my full health with almost full iron armor (gold helmet so piglins wouldn't attack me) and full food down to 2 hearts. If I tried to move or get out of the hole I was set on fire again until I was killed by it. The chat didn't say how I died I just re-spawned. I went back for my inventory to find a few blocks and the pork chop I was eating. My tools and everything else were gone as if they were burnt, but there was no fire or lava near where I died. When I tried to leave again I was set on fire like the time before. I also placed a block of netherrock down and it immediately had a fire lit on top of it. I let myself die on top of a magma block because my inventory was nowhere to be found. That death did show up on the chat as "discovered floor was lava". In the attached picture I was in the corner where the blue circle is.