I got a Liquid Vent Obstructed error for a working shower. The liquid vent was where this system exits to is above water level. Dupes were still able to use the shower, though.
Steps to Reproduce
I think this happened because I accidentally demolished a pipe when I replaced the outhouse with a lavatory. The error did not disappear even when I reconnected the pipes. Oddly enough, only the first shower got the error.
This issue has not been confirmed by a developer yet.