Switched the humidifier to absolute humidity with a 60 s minimum on/off and it’s been flat for 3 hours: temp within 0.3 C, RH within 2 %. With everything on one chart I could also see the mist hit the temperature about 20 s after humid_on went to 1, which went straight into the report. My supervisor wants the dew point version next, of course.
Timestamps in UTC or it didn't happen.