Last Saturday I was shooting my 9mm RR at the range.
With original Colt 32rd mag - no problems at all.
With IMI Uzi mag modified: jams and stove pipes. Each second or third round. I only loaded 10 rounds.
I notice that though the two sit at the same height, there is some forward/back play with th Uzi, which may contribute to the problem.
I also noticed that the South African mags (no back spine - no star of David)are wider front to back and have less play. I did not have one to shoot with.
Has anyone tried to add a spine out of some slick plastic to make sure the Uzi mag has little play? Does anybody have recommendations?

Problem is follower related.  It is either binding or angle is wrong.  I have a bunch of converted Uzi mags and they all work fine whether they are loose in the mag blocks or not.
Load up a few rounds and compare the loading angle to a working mag.  Chamber the first round and then manually eject it and don't let the bolt go forward, look at the next round in the mag, bet you the round is at a weird angle or not completely up.  The Uzi mag uses both sides to feed so check the next round also.

BTW, the "star" on the IMI mags are not the Star of David.  The Star of David has 6 points, all the stars on the IMI mags are 5 points.

Hail Mary:
You are correct the Colt angle is steeper and seems to better position the round for feeding... How can this be changed on the Uzi clip?
Your are 100% correct on the Star - it is not David's.

Bend the follower legs slightly to change the feed angle; don't bend the feed lips as they are very hard.  Check the feed lips for cracks and burrs; there was a large batch of IMI 25rd mags that were sold 2 years ago by a distributor that had cracks in the feed lips.

Should the angle match Colt's angle? Or, should it be trial and error little by little until it works? Any angle value?

I had problems with a bunch of converted Uzis and tracked the problem to my ammo. With 115-grain they ran fine, but with many 124-gr and heavier bullets, the fatter nose caused jams.

All the ammo ran fine in my Colt factory mags. The Uzis, as noted, had more play front-to-rear, and I suspect that "swing" allowed the feed ramps to tilt just enough up or down to hang up the fat bullets, but let the 115-grainers feed fine.

Match the angle to the working mags.  I think it's 4 degrees.  The Colt mags are a direct copy of the Uzi mags.