I've watched a good number of Rangers matches this season (I'm in Scotland, but not a Rangers fan), and it's been a lot of ups and down. Probably more of the latter at the moment, but it's minor errors or slips rather than anything fundamental from my perspective. Such as tonight he gave away the free kick the resulted in Aberdeen's first, and might have been able to do better at their second, but these things happen. A lot of the european games were tough as well, but Rangers were just outclassed all round.
I think the biggest challenge is lack of consistency and the situation Rangers have been in. He's never settled in either midfield or defence. Any time he gets games in midfield, where he seems to have better performances, he's either needed back in defence, or something else happens. For the past few months, Rangers have had a serious injury crisis in defence, with only an 18 year old and Sands at times any recognised defenders available. They started their last match with Sands and another central midfield player in defence alongside a young inexperienced left back. None of this helps his development, at least short term.
A change of manager probably not helping consistency either.
But I think if you take the whole of his performances I've seen this season, there's a lot more positive than negative. He's been comfortable in a lot of games and among the better performers in terms of stats. Maybe not just in the eyes of many Rangers fans who expect comfortable wins every match or there's a crisis (which of course needs a scapegoat).
If he can build on the positives, I'm sure he'll keep progressing. Just maybe not at Rangers.