When sims are supposed to be nude or have more revealing clothing the salmon colored (hideous btw) underwear from CAS body edit mode is showing.
Edit By Crinrict: Adjusted Title fit bug report at ...
Ideas
I know how its trigger.
You'll need a sim using the shower/bath or being in the nude, save and exit then re-enter the save, after that any sims in that save will have clothes (the kind when you unselected clothes from cas) on while they are showering. Some people will say it cc related, but it's not, I did test it on a new save with cc turn off.
And also is confirmed to be a base game glitch, no packs.
I moved my sim to another house and he had a shower the next day. I only saved but did not exit and he was wearing his underwear while he was showering. I'm on playstation 4 pro