I have NO mods, and little custom content. I had had this bug since World Adventures. I once took a trip to France, the fireplace caught fire, kept sparking. I went home early. Waited a few days, went back to France. It was still burning.
Last night, I had a bad one. I let it go in REAL time from 10pm till 4am, as I wandered off for bathroom, munchies, read a book, and more. I caught it when it stopped for a few moments. Deleted everything on fire. Removed floor tiles. Put a wall up. Later put new floor tiles back. Had about 9 Sims die of fire or starvation. 2 others had Loser or Unlucky, and the Grim Reaper kept bringing them back to die again. The fire alarm would go off, the firefighter would come over, would say "I can't reach it, hopefully it will burn out on its own" even after I removed everything in the room! What the heck is it catching on?!?
The fire raged on for over a Sim week before I got tired of watching it. I remember for Sims 1 and 2, there was a cheat to reset the entire lot. Is that cheat still out there? Might it work?