I’m afraid those were my two best shots. At least you know it isn’t anything to do with HDMI.
Have you ever tried a burned dvd in those blu ray players and have it work ok? Making one in a computer isolates the players from the dvd recorder. If you eliminate compatibility of burned media as a problem, then you are down to the manner in which the dvd is made in the dvd recorder.
Which was why I recommended FixVTS on a dvd made in the dvd recorder, as it will adjust dvd structure so that it complies with strict dvd-video specifications.
When you say you are using a video enhancer, do mean you are using something to get rid of Macrovision on commercially made VHS tapes?
But looking through your post again, the part that really baffles me is why it works on a dvd player, and not in your blu ray players. There really shouldn’t be this great difference.