I have EPL Stage 2 on 2017 Audi S6 and APR Downpipe on OEM Sport Exhaust. O2 spacers were installed but I still threw a CEL. Recently I noticed some strange issues including:

1. At WOT usually from a roll power delivery will momentarily stop bear 6000/rpm before resuming and then CEL will start blinking.

2. When driving around town with moderate throttle car will have trouble accelerating and exhaust will sputter a little. CEl will star blinking.

Any idea what this could be caused by?