Me too - ever since I tuned up one day - tuner said everything was fine. Started playing - the A string sounded way off. Check it again, tuner says fine. Play it again - sounds off. It wasn't until I cranked the string about a half turn up, then down that the string sounded fine - tuner still said it was fine.
I know this makes zero logical sense but it spooked me and now I always do my first tuning so I can hear it. Subsequent mid performance tunings I do silent.
Are you running it off a battery or power supply? I could be that the battery is/was dying.