Well, there's no error message to go by, so, there's really little we can do.
I have Mega Man 8 and it still plays in my PS3 so I tested it by attempting to read it in ImgBurn in my Pioneer 2209 BD drive. It failed to read, but I was getting returned error messages. L-EC Uncorrectable errors, so it could be that my disc is not good anymore and is only readable enough to boot on my PS3 but not play all the way through. However, given the fact that you can't read Mega Man 8 either, it seems to more likely be a case that, for whatever reason, ImgBurn can't read Mega Man 8. Which would indicate that some PS1 games can be read by ImgBurn and some can't, since you got some discs read to image files and some not.
I ran another test on another Capcom game from a few years after Mega Man 8, Strider 2. ImgBurn read both discs to image files. This backs up my idea that some PS1 games can be read in by ImgBurn for whatever reason and some can't. Also backed up by the results you achieved, where some discs would read and some wouldn't.
Why you got no error returns is something down to your drive most likely.
And it seems to be dependent on the drive, too. I tried reading the disc in my LG WH16 BD drive and it never completed analyzing Track 2 from Session 1. Even after 10 minutes, where I gave up because if it won't do it after 10 minutes, it won't do it at all. The Pioneer drive seems to be failing at reading Track 2 on Mega Man 8, if I had to hazard a guess.
It does seem that certain games can't be copied with certain combinations of hardware and software. I tried reading an image in Roxio NXT 4 on Mega Man 8 and it crapped out at the same place ImgBurn tried to read it at.
Now, these "bad sectors" may be Playstation's copy protection method. That it looks for purposefully bad sectors as a way to check for legitimate physical discs. However, I thought these bad sectors existed beyond the end of the disc to look for. Plus, it doesn't explain why Strider 2 worked and Mega Man 8 doesn't, except that Strider 2 is newer.
However, I'm more up to thinking it's down to the individual games in question and the hardware and software you use to read it. For instance, ImgBurn and Roxio failed on Mega Man 8, but UltraISO DID read it to a BIN/CUE file. Although, where it crapped out in ImgBurn and Roxio, UltraISO "paused" at the same place, thinking about it. But, it did eventually get an image file read. How accurate/playable that image is, though, I don't know.
So, if you have UltraISO, try that. If you don't, UltraISO isn't freeware.