Hi, I hope it's not too late to answer this.
I have the same problem since games I burn are read and work on computer (with emulators of course) but not on modded PS1.
As long as I know, the problem lies in the burning process, 16x is too fast and the highest degree of certainty comes with 4x. PS1 can't properly read high speed burned disks. Probably the disk label has some influence on the issue, but I think the burning speed is the main problem.
Anyway, I hope you have solved your problem (or you will).
