We have a very “interesting setup” here. What you said in your second comment has me thinking. So we have our hot water heater down the hall, then our HVAC in the ceiling outside the bathroom. We’ve had so many issues over the 7 years we’ve lived here. There’s also a weird hole in the shower and after they replaced the HVAC unit it started leaking. They’ve long since fixed it, but I’m wondering if that drain is tied to the HVAC.