You are not alone in frustration with AMC6! As was discussed last month when you raised the same issue, it appears the problem must be with the source or transmission. While my AMC6 LNB is off-centre, AMC6 has always been a very strong satellite, and usually on the mux you are talking about I get in the 60s on my Pansat. However, if the quality drops to around 45 (like it did tonight) I get serious pixelation. Usually a 45 is good, on any other satellite, and I don't have any problems unless the quality drops to around 25 (and some are fine even lower).
Solution? Don't know, but I have deleted the channels, deleted the transponder, and re-scanned without any improvement.