July 2021
My Sim always catches on fire after getting up from peeing in the toilet. She is a Child (girl) and a Spellcaster. This did not happen when the family lived in Strangerville. After they moved to Willow Creek, it happens every time she uses the toilet.
July 2021 - last edited July 2021
@racheyisabean Do you have the Pack Eco Living? Burning or exploding toilets are part of the composting container that is installed in some of the toilets. When you have upgraded your toilet with a composting facility and do not empty it regularly it even might spontaneously combust. When having a composting container installed empty them at least after every third or fourth time your Sims used it.
In Strangerville the Eco Living game play doesn't work like in the other worlds.
Have fun playing. 😉
July 2021
What @Trismagistos said. This is almost certainly a toilet upgrade from Eco Lifestyle. If you don't empty the composting container it catches on fire, but you don't even get the option if you don't have an insect farm.