Sticking followers? I've fixed dozens of them. Sometimes the cause is bad heat treat of the mag tube that causes it to warp slightly, sometimes it's a burr on the tube at the top that catches the follower, sometimes it's a poorly manufactured follower that is lopsided or just plain wrong in one dimension or another. These are all fixable with some effort but generally not worth the effort unless the replacement cost for a new mag is prohibitive or you enjoy a challenge.
Me, I'm a glutton for punishment and take a poorly functioning magazine as a personal insult. Here's a magazine that wasn't functioning correctly and drove me crazy trying to diagnose it. It was exhibiting failures-to-lock back on an empty mag. Eventually, I discovered it had a tiny burr that was catching the follower at just the right time to cause the problem. The burr was so small I couldn't feel it with my finger. The way I found it was by gently, slowly pushing the follower up the tube until it hung up.
This picture shows where the follower got hung up. "C" is pointing to the area where the burr was located.
This picture of the follower shows the slide stop engagement tab "A" while "B" is the spot where the finish was rubbed off due to repeated contact with the burr.
The last picture is another view of where the burr was located at the tip of the arrow inside the tube.