It's almost always a bad idea to mess with a working system. If you can, put everything back to the way it was to confirm if it is working or not.
You can usually tell if it is a buffer or magazine problem by how it feels during the last round. So if the magazine is not pushing up on the bolt release, you'll usually feel the last round slam a bit harder than normal because nothing is slowing down the bolt. It'll feel exactly like if you unloaded the rifle and pulled the bolt back and let go and it's slamming forward without anything stopping it.
However if you're feeling a sort of "hump" on the last round like something tried to stop but it kept going, that's because the magazine didn't fully raise the bolt catch in time and only partially raised it.
You can also tell if after the last round, if you pull the charging handle back is it locking the bolt back or is it slamming forward even with the magazine inserted?
Usually when it's a magazine problem, the issue will be that the bolt catch isn't able to reach the follower. Sometimes in magpul pmags they'll do this with certain gen of the rifle but in your case you're using a totally different brand.
It may also be a buffer problem where it is cycling too fast for the bolt catch to raise in time. And it may be a combination where it's cycling too fast BUT it's also not able to raise it quick enough because the spring isn't as strong due to the magazine.
Best way to figure it out is to study the last round hold. If it is one magazine doing it, I wouldn't worry about it but if it is a particular brand of magazine and you have a lot of them, then perhaps it is worth investing some time. For starters I would put the magazine back to its factory configuration and go with that.
Lesson here is to change out one system at a time in your build.