I have that same issue trying to use FireBrandX YT method for optimal timings. (Where you set it to 320×240 optim, then adjust the phase and H sample rates)
Worked perfect on NES and SNES but on PS1 I can never get rid of some shimmering in a corner unless I Just use 4:3 mode instead of 320×240.
Aside from that I keep dropping sync during gameplay (not menu switches) on several PS1 games (FFT, FF7, Metal Slug X so far)
Super annoying 🙁