There seems to have been a rash of such comments recently usually with a 598/568.2 combo - check out the postings by eddiewww for example. Speculation was that the 568.2 was the cause - your observation makes it more likely that the 598 is guilty. Is the problem heat related?
I hope Meridian get to the bottom of this as I was thinking of doing just what you have done and getting a 598 in place of my 596 and then upgrading my 568 to .2 status - maybe its time to think again
Graham

Meridian Owner since 1991