2018 Q7 Rev counter

[V12 Migaloo]

My 2018 Q7's dashboard is digital, and rev counter went red for the drive back from Eurotunnel this week.
Instead of the last 2 digits being red, all of the numbers turned red... speedo remained the same, the morning after she was back to normal. No change in performance or anything before or after... Anyone got any clues what this may be...? Was it a DPF clean, if so, I've never seen it before in 4 years...