Hello Sports Fans
Started monitoring posts today. Been a long time Line6 user. I have the 1x12 MKi , MKii, 2x12 MKii, M9 and shortboards FBV MKi and MKii.
The harness cable located on the DSP board near input jack is notorious for coming loose. This loose harness cable will give rise to the symptoms you are experiencing. Once snugged in I use a strip of masking tape along the seam to hold it in place. More convenient then a dab of super glue, nail polish, of gum.
Bigmose