I've never experienced anything like this. Last Saturday, we played at an outdoor venue after a thunderstorm along with normal high humidity. The 3rd set I had a couple of instances of fretting out. I thought it may have been my fault. The last set it happened more and more. I had to ditch it in order to finish the night. The next day I pulled it out and the bass was unplayable. I've let it sit out of it's case for the last few days and will set it back up for a gig this weekend. Would moisture do that in such a short period of time? I've used this bass plenty and it's never acted up!
That's bizarre. I hope it resolves itself back to playable condition. High humidity can certainly play havoc with wooden instruments, but that seems extreme, as if the humidity perhaps only triggered some preexisting underlying issue.