I thought you stopped getting those after level 1,000. In fact, that’s what happened (or rather, didn’t happen) over the past 100 levels or so. But now, as I was completing Urskaya quests, I leveled up to 1,135 and got a mastery level.
I think Rasper reported that he got a single additional mastery after the Unity update and then it stopped. Until they announce that they are going to allow additional masteries on PC/Mobile, I would say it’s a bug report.