My bench press arch gives out after a few reps and I can't fix it
I've been trying to get my bench press form right for a while now, especially keeping a good arch for more strength. But every single time, around rep three or four, my back just goes flat on the bench. I moved my feet around, switched my grip width, and even took phone videos to check myself. When I start to get tired, everything falls apart and I lose all tightness. I looked up stuff online from coaches I trust, but none of their advice stops this from happening. Does anyone know a good way to keep your arch solid through a whole set? Maybe there's a simple drill I haven't tried yet. I lift alone most days, so getting help is hard, and it's really bugging me.