EPU in Airbus gone crazy
So flying along in my Airbus the other day with both FMS in IRS/DME/DME due GPS jamming. But picking up plenty of rad navs and position is updating nicely, both FMS have EPU under 0.5nm. All of a sudden FMS 1 goes crazy and EPU shoots up to 16nm in around 30 seconds. ND shows us 6nm left of track. Luckily AP2 is engaged so it's following the good side. Around 2 minutes later FMS1 settles down and goes back to 0.5nm.
Has anyone seen this before? Any ideas why this happens? A software bug or is there another explanation? Could a malfunctioning Navaid cause it?