A rollback means something specific. Semantics do matter here and they aren't the same thing. New content has re-locked (chapters, boss pit, mountain, challenge) and the ability to progress to the next level cap has been locked and those who hadn't gained a level seem to have lost XP, but those who already attained new levels did not lose them. Those who had gained levels cannot promote heroes past the old cap however (so if they are level 102 but the cap had been 100 they can no longer promote heroes past level 100).
We have already flagged this up to our contacts. We know this is affecting all servers that just had a cap increase (7-11). If you notice something additional that is not in the above list please add it. This is impacting everyone on those servers, so five servers worth of some variation of "Me too and I'm mad" will make it hard to pull additional important information out. We totally understand that people are fuming and we will do our best to get info out as soon as we have it.
UPDATE: This looks like it has been resolved (at least on s10 and 11) and folks have not lost any XP. We will try to get confirmation that it is fixed.
Update 2: All servers are reporting that things are ok. If something did not come back correctly please contact CS right away.