My CS80 had this problem for some time now and I'm starting to think it might be heat-related.
So some voices tend to randomly go dead especially in the bank 1. It is difficult to diagnose because when I take the card out to inspect they sometimes come back....When I screw the card back sometimes they go dead again. Also when I leave my synth on ant it's hot some voices die and come back again when cold..... I live with it but I would like to get rid of this issue once for all. Did you guys had the same problem before? Maybe it is not M card problem at all but TRG board for example?