@YeeHaw984, have your Sims upgraded the toilet to either have the Composting Container or upgraded it instantly to apply all of the upgrades (which would then include the Composting Container upgrade)? 🤔 If so, that is most likely why your Sims are catching on fire since compost is made of organic material, and organic material is combustible! I think this upgrade has a chance of causing fires if you don't use the compost it makes. 🤨
If you do have the upgrade, you can try to test it by placing a new toilet without the upgrade on your lot and see if the same thing happens. 🤔
Please update us on what happens! 😇