If it's like the Pretensis, a fix is a square of ABS 1mm plastic. This is made to match exactly with the rectangular hole through which the probe comes, and of course has an exact hole for the probe. You make it a push fit into the hole, with a tiny bit of glue on the edges. There was just enough metal to make it a flush fit and still allow the probe to come forward the maximum allowed.
This makes it so that a pellet coming backwards cannot go into the mechanism as the skirt is bigger then the probe.
Apologies if this is not suitable for your gun. And yes, the JCHU mag is excellent.
Also. polish the end of the pellet probe so it is less likely to hook/jam onto the pellet.