Serious, I would relocate it as you do not want a bathroom without some air circulation as the moisture would lead to humidity and possibly mold issues

They would have a moisture meter and should be able to trace to the source.

Mold requires two things: moisture and a food source (typically dust).

Are you sure you have a foundation warranty and not a moisture termite warranty?  

Those closets should be fire rated and have makeup air to each one. they should have a layer of 5/8" drywall on the walls with all joints sealed. any penetrations should be sealed with Fire caulk.

., assuming there are no code issues here, I don't think this will affect your ARV or sell time one way or the other.Make sure you do a good inspection of the sheathing from inside to make darn sure there aren't any leaks, penetrations, or other issues.

Washington is very rainy and I need to do these repairs now so that moisture can dry through the summer @Nathan G.Thanks for the response!  

If you hit one or two ripe markets hard you can be the expert there and really penetrate the market.

On inspection, evidence of high moisture was noted in the basement.

There's no dripping/leaking going on, but there is definitely moisture on some parts of the walls.