Ditch the horseshoes and go with leaf switches for the drop targets. Alien Poker works fine like this and it's more reliable. I converted mine. I bought a 5 bank that came from Jungle Lord, I think.

It's been a long time since I did it, but it likely involves soldering all the wires over onto the switches and potentially all the coils depending on how much you swap. The JL drop target bank comes with a bracket where the switches can sit, so potentially just that bracket can be swapped in, making it so there's a little less wiring work.

There's a post from someone who did it here:
https://pinside.com/pinball/forum/topic/alien-poker-switch-matrix-problem#post-2263724

This is the reason AP can be converted to leaf switches, since it doesn't rely on momentary contact as the target falls. It relies on constant contact once the target is down, which is better suited to the leaf switch setup, in my opinion. Games with horseshoes that rely on the momentary contact would not work in a leaf switch conversion - so perhaps AP is among the few games where a conversion like this can happen.