I've been dealing with the same thing on one specific Snapshot in one specific preset. I have an Essex A30 patch which functions perfectly fine in Snapshots 1 & 2 (Clean and Crunchy Breakup respectively). When I go to Snapshot 3 which has the amp with full gain and master volume, the sound will slowly choke out similarly to if the input signal is dropping steadily. Eventually it'll reach no audio at all but often switching Snapshots seems to correct it momentarily as going back to Snapshot 3 works perfectly fine. Until it does it again. I once left it on this Snapshot for an extended period and the audio was gone entirely from that and other presets. Luckily mine worked again after turning it off and on again.