1SOW --- Thanks again!
IDescribe --- Good thought on the mag spring, but it is nearly impossible to assemble the mags backwards. The design is such that they are somewhat polarized, making bad assembly almost impossible, unless a hammer is handy. :-)
Guess what? It happened again, right out of the chute! Fired 5 rounds, then mag went into vapor lock! My take on it ? the jam cost me yet another stage of fire. The sand seen in the mag is after hitting the ground, other wise, mag was super clean as usual. I preserved as much of the failure as possible, including the sand.

Got home and cleaned the mag thoroughly, measured and decided to squeeze the mag by .010 right at the point of jammed rounds. It now measures .855 wide instead of .866. I do have some vise jaw dents in the mag ? which look awful, but if it works, fine. Ready for the next match on Thursday.
Spring comparison: Image is of three mag springs. The one in the center is the set-up that came out of the failing mag. It does have a curved set to it, strange, but somewhat expected.
Spring set-up on the bottom is new, not yet installed in a mag. Center and bottom set-ups are from the CZ Custom Shop. I have one magazine that another of the CZ Custom Shop springs in it and it works fine, not 100 percent but I'm not afraid to use it.
The top mag spring set-up is standard CZ factory set-up as received. I have it in the big stick mag now, along with the ?squeeze? job. BTW, wouldn't ya know it, the failing 26 rounder mag number is ?13!?

All for now.