I doubt it's a media problem. RAM discs never really "erase" as we think of erasing, say like a RW disc. All they do is erase the file tables. Same for formatting. You could try using a PC drive to do a full physical format, (takes forever), but you'll just be doing a work-around for a faulty recorder.
I've never seen any trouble with discs formatted or erased in my Panny. And, if you're using Panasonic RAM discs, how much can they say about the discs?
In theory, a RAM disc sector does not get written unless it passes verification. Doesn't sound to me like your re-written discs should be passing verification. That simple fact alone should spell a bad recorder. Either it's recording faulty discs, or it's not able to read a well-written disc.