Normally used on the 28/29/X29 routes to Fakenham, Dan High managed to get a photo of it leaving Norwich Bus Station earlier.
Unfortunately no information on the destination screen but the other photo from Kieran Smith definitely confirms it.
My contact at First Norwich tells me it was the sinkhole in Lowestoft causing severe disruption to services, resulting in no X2/X22 buses for more than an hour out of Norwich. Hence the additional working which was fully loaded. As a goodwill gesture First didn't collect any fares due to the long wait suffered
My thanks to Dan for the original photo, Kieran for the confirmation and First Norwich