Sometimes when folks go to hit the magazine release, they shift the weapon in their hand slightly to make the button easier to reach. In doing so, they brace their first or second finger on the other side of the frame, to support the frame while they press the release. Occasionally, one of those fingers will end up against the other side of the magazine release button, and the person will push on both sides of the button at the same time, and wonder why the magazine is not popping out. I've done this myself, in front of a group of competition shooters, no less, and it can be rather embarrassing. If you push on the mag release one time and it moves freely, and then when you try to use it later it seems stuck or jammed or sluggish, make sure you are not accidentally pressing on the other side of the button at the same time.
As for the magazines popping/jumping out of the gun once the button is pressed, you might try wiping down your magazines to make sure the mag bodies are clean and free of grit. Some folks use chemicals to make the mag body slicker, like Armor All treatment/protectant, but I've never used it myself, so I can't endorse it personally.