This happened to me three times before I finally realized that it was in fact a bug and recorded it because I wasn't looking at my health before I died (because I didn't think it was low enough to be an issue seeing as I hadn't been hit yet). It was a one hit me when I was at full health and wearing full diamond armor, I attached a clip named "Blaze Glitch." The blaze was probably less than 5 blocks away and I had no other status effects in the occurrence that I recorded.
I was playing on a Realm that I own using a Windows 10 PC
The most frustrating thing about this is that conduits and beacons have a very restricted range and it completely messes up my design for bases. It also is inconvenient for automated processes such as farms, furnaces, or other time based tasks.