Update: my deck railing went from wobbly to solid after I found the real problem
My deck railing in Bakersfield felt loose for about 8 weeks and I kept tightening the same 4 bolts on the posts. Finally pulled a board off and saw the lag screws were going into rotted wood, not the rim joist. Swapped them for 3/8 inch through bolts with washers and it locked up in an afternoon. Anyone else had a fix that felt obvious once you saw what was actually behind the board?
So you had 4 bolts you kept cranking on for 8 weeks and the wood behind them was soft the whole time? Idk man, that sounds less like a mystery and more like something you'd feel out pretty quick if you put a wrench on it and it never got tight. Lag screws into a rim joist shouldn't spin loose like that, and if they did, poking around with a screwdriver would've shown the rot way earlier. Through bolts with washers are the right call, no argument there, but calling it a hidden problem when the wood was mushy enough to swallow a lag screw seems like a stretch. Maybe it's just me but a wobbly rail usually has an obvious weak spot if you look for it. Not saying it wasn't a good fix, just that the railing was basically telling you the whole time.