It’s been noted by others in previous reviews online that the Rival Pathfinder doesn’t like older magazines. The reason? It latches onto a plastic ridge that was added in 2019. I still have a review to write after an upcoming war (and testing), but for now we have a solution.
The magazine catch mates with that surface in particular, and holds the magazine up far enough to engage the ball release button. Original Rival magazines, lacking that extra plastic, sit too low to engage that button. With the shims glued on that surface, you’ll be able to use the magazines in the Pathfinder.