Could be, I’m not familiar with how the sync is generated. But have you seen them tested with SCART, or just VGA? VGA syncs fine for me, but the noise in the video signal is just too much of a drawback.
Would you be able to help determine, from a technical standpoint, what might be causing this kind of noise/jitter? To get a good video sample of the noise, I deliberately offset the H. samplerate by a few values and sharpened the video output: https://www.youtube.com/watch?v=a-PrBT-P2w0
You can see that the vertical bars are so jagged that there is no vertical slice of the screen that is free of noise. So even with a perfect samplerate and sampling phase, bits of the screen are in constant horizontal jitter. Here it is with a perfect samplerate and phase, again sharpened to better display the noise: https://www.youtube.com/watch?v=YTDmXDWRyMw
Applying a video LPF of 9MHz (EDTV) eliminates most of this noise, with the exception of the largest spikes.