I realize that there isn't much to go on yet. I'll update this report if I catch it happening. But I've noticed that occasionally, my Sim will use a toilet in one restroom, and will then go to a sink...
Ideas
I've been noticing that as well whenever my three young adult Sims are spending some time at The Blue Velvet Nightclub. I think this also occurs at their residence (2 floors plus a basement that I've added). I have Windows 10 and is using both mods and CC.
My (young adult) Sim has 2 floors plus a basement. She added the second floor for her master suite and a game room, and added the basement for a TV/movie room.
Anyway, it's just weird when she walks up or down a flight of stairs to use a sink, when there was a perfectly functional sink in the restroom where she used the toilet.
