Check for loose wires on the kick up solenoid.

Had a similar problem with mine. Turned out the balls in the trough were not moving forward when a ball was being placed in the shooter lane. The thing that loads the ball was not returning all of the way and holding the other balls up. Spent a lot of time looking for switch issues till I found the real problem.

I recently refurbished a swamp kickout, and I had found that one of the switches was loose. You might want to remove the swamp kickout, manually check the switch levels, listen to the clicks, and check the switch levels with the system tests. It's good to clean the whole system out, and perhaps swap out a new solenoid sleeve while you are in there as well.

You can see how filthy this one was was here, all that hidden grit is bad for the balls/PF.
https://pinside.com/pinball/forum/topic/tech-taf-swamp-kick-out-weak

Also -- you might want to drop a note in the TAF owners club looking for help (here).

-mof

https://pinside.com/pinball/forum/topic/mod-for-taf-swamp

Had same issue...fixed it like this...

And to echo what others said, I had done a complete PF swap on my TAF back in October and I found one out of 100 balls were getting stuck but at first I thought I had a flaky switch. I put in new weldments and the one had some spot welds that needed filed down. When the ball would the spot just right it would hold it there as crazy as you'd think.

So not that you have that issue, but could be something physical so check the easy stuff. I do like Rlerman's easy fix too!