The region code being removed shouldn’t pose a problem, I’ve burned hundreds of discs the same way. It just makes the discs region-free so you can play them on any region player.
With the latest version of DVDFab Platinum, it’s possible to set the burn speed exactly (for example, to 8x rather than just “recommended”), so I’d suggest setting it to 8x.
If that doesn’t work, a different brand of media may be in order - Memorex disc quality can vary since they use a variety of manufacturers, then just slap their name on the packaging/discs.
Maybe other members will pick up on something else