When I'm making a Blaze farm on two Blaze Spawners in close proximity. I drank some fire-resistance potion during the construction so that I don't take damage from the fireballs.

However, when I was cleaning Blazes spawning from the second spawner while I was working on making the first spawner a farm, my fire-resistence faded for a second. Just before I notice the fading of fire-resistence. A blaze shot a fireball at me, which one-shot me. The proof that this is a one shot is that when I picked up my armors (which were all newly made), they were all deep in red, indicating that several hundred damage was dealt at once.

This occurred to me again shortly after, I drank another fire-resistence potion and cleaned up the blaze hordes, and finished building the first blaze farm. Just as I went to the second spawner to make it a farm, a blaze spawned. Just as I was drinking a fire-resistence potion but before I finish drinking it, the blaze one-shot me again. I was wearing the previous armor that were badly damaged by the first instant-killing fireball, and this time they were magically all at maximum durability when I picked them up.

The third time this happened to me is after I finished the blaze farm. After the two farms finished, I discovered that they were not working at full speed, so I knocked a few blocks to increase the spawning speed--at the cost of being rarely hit by fireballs. It initially turned out fine (I haven't determined if the glitch really existed), but after about an hour, I got hit by a fireball and was one-shot again. This time, all my armors instantly broke, and the chest plate actually had fire-protection on it. All three one-shot happened after lots of fireballs were ignored by the fire-resistence effect or blocked by wall.