This was marked as MCPE-19535 before (also was reported multiple times even before that, it was just the most recently closed.) It was marked as resolved, but the issue persists. Seems to only happen in Realms. Blaze attacks, shatters all 4 pieces of Protection IV diamond armor, kills instantly. If this is intentional, it shouldn't be. Maybe for your next superboss, but not this fairly common Nether mob.