Appliances break very easily

I thought of taking proper notes on the frequency for better reporting, but somehow my bathroom no longer break frequently as before. Currently I only have 3 sims in my household and the bathrooms (all upgraded) only broke down once in 1 sim week. Previously I had around 5-6 sims in the household and my bathrooms would broke down every 2-3 days.

Regarding goofball prank and reliability, I stopped playing with Kim-Lewis household once Olivia (goofball) aged to teen, and her mischief was at level 2. I doubt she or other sims doing it as when I don’t instruct them to do anything, they either went straight to fireplace to keep warm or go swimming. And no one in Goth household have goofball or other mean/evil traits. 

I checked both Goth and Kim-Lewis household plumbing stuffs reliability, lowest is 5, highest is 8. And when I first played with the households (no upgrades), I would have 1-2 stuffs broken every 2-3 days. I now mainly play the Goth household, in the beginning, the bathroom sinks and toilets (all reliability 8) keep breaking down every 2-3 days. I upgraded all of them but I still need to repair them like 2-3 times a week (when I still have around 4-5 sims in the household). The difference was like, before upgrading, I would have one item in both bathroom broken, after upgrading, it was like only one item for the whole house.

I think I will make a new save in the future just to test how many times before somethings break for each reliability scale.