The fireguard upgrade is causing fires, since the last patch. I had a sim living in VIII Landgraab Apt. After the patch I had a lot of fires including 5 fires in 2 sim days, which is double what I have had since playing Sims 4. I had her move to the penthouse in the Arts district and installed a fire after I had her upgrade it, I sent her to the festival outside. While at the festival I had her light some fireworks and was notified of a fire. I was searching the festival area but could not find a fire, so I checked her apartment and found the fire, it had spread into a second room through the wall, from the bedroom it had started in. My sim lives alone and as the fire had autolight as well as fireguard, I have no idea how it started.
I do use mods, but have removed my mods folder, repaired the game and started a new game. I moved a sim from my library with the needed skills into VIII Landgraab Apt had her upgrade just 1 of the fires, as soon as I had her walk into the room it caught fire. So it seems very easy to reproduce. The other fire in the apartment that I have not upgraded has not caught fire, even though its been lit since she has lived there.
