I have had that issue on the LEFT side a couple times
FIrst time it was the front left turn signal (not sure if it was the side or front lamp) removed and replaced (Same bulb) and all good
2nd time it only happened when towing.. I Improved the ground connection at the tow connector (Motor home end. don't know why I tried that one first.. and last) and all good.
In all cases the "Bad Ground" is the answer.. Full explanation is more than I care to type today. >Been a long day and 2 more coming.. Only fun thing is I'll grab a free hotdog Wed :).