If that turns out to be the problem,then I'm glad I could help.
I had a similar experience with a dish a few years back, where I could tune in the 110 and 119 but not the 129.
I could swing the dish around and get the 129 but would loose the 110 and 119.
I messed with that for more then an hour and then had to drive 40 mi back to the shop to get another dish.
You don't forget installs that go that bad.
In this case, My pain is your gain
Now I inspect the flange on every dish I load on my truck and I also carry spares now (at the time they wouldn't let me, something about it being an inventory thing)
EDIT
I'm going to add another thing there is a pin in the center of the skew plate that can slip out of the hole that centers it.
This too would make it hard to point the dish...had one of those just yesterday for a guy in a camper who had pointed his own dish many times before but couldn't figure what was going wrong this time.
BTW I showed him the "dish pointer pro app" and was so amasied that he downloaded it to his I phone...said quote "you just saved my marrage"