Same problem for me!
I ask my sim to perform any of the upright shower functions (brisk, thoughtful, sing, etc) in a combo shower/bathtub. Everything animates as expected but no timer forms around the action icon so the sim showers indefinitely, yet the hygiene bar does not improve- in fact it continues to decay. Inevitably I give up and manually cancel the action and my sim leaves the shower dirtier than when she started showering. Ironically, if she was supposed to get any “boost” from the shower type selected (for instance, inspired for singing in the shower) she gets the matching moodlet as if the shower had worked perfectly!
As an additional observation, the combo shower/bathtubs are now showing options not usually available to them: mid bath, bath with salts. I tried using these and they function perfectly. In fact, all the “bathing” options perform perfectly, with timers, increased hygiene, and appropriate moodlets and boosts. Only the upright options are misbehaving.
Not sure when the issue actually began, since the December patch came out about the same time I added university and because most of the lots I play don’t have combo shower/tubs, so I didn’t notice this until moving into a gallery downloaded lot for student housing which happens to have combo shower/tubs. So I can’t isolate when the issue actually started or what caused it. My current work around is daily citrus baths to keep my student sims focused up!
