Digital pedals delay the signal a bit (A/D and D/A conversions) such that it will be out of phase with your straight through analog amp path. Parallel loops are a hangover from the past when most pedals were analog and it was thought that having your main signal un-effected would maintain purity of tone….nice in theory but not with digital. You need a series loop (or parallel set to 100% loop, which amounts to series). Then the dry signal goes through the pedal and actually gets digitalized as well as the processed part, so no phase problem.
