Welcome to the wonderful world of AI mags. They're still the standard, even though every other part of the gun has moved on. It could be any number of things:
Might be tolerance stacking, all of your parts may be good on their own but drift to one side of nominal and now it won't work. Could just be a bad AI mag, which happens al the time, they're not super consistent. I own about 2-dozen rifles that take AI mags (5 are actual AI rifles) and bad mags on occasion are part of the deal, even with new ones. Stock inlet could be too shallow pushing your magazine presentation height down, mag catch on the bottom metal might be too short to push the magazine catch tang high enough, could be weak spring pressure on the mag catch itself. The mag well might be too long front-to-rear, causing the front of the mag to nosedive (this is why the AIAX magazine has a front locking lug), which is very common.
I would start with the easy part and try to apply a small (one-finger) amount of pressure to the forward bottom edge of the mag and see if it feeds. That's a sign of the mag riding too low in the front. If that doesn't work apply pressure from the center and see if that helps (accounts for mag catch height). Barring those, try a new mag. It will have to be a metal mag to fit in a Tikka, Accurate Mag makes a good one that are usually readily available.
The line between these conversions working and not working is very, very fine anyways, so a tiny change might make it work fine. Once you diagnose the problem, then you can get into fixing it, hopefully with as little ass pain as possible,
