Getting bathtub spout seated properly

[H.Corning]

Hello. I hope you are well today.

I removed our tub spout to soak away encrusted minerals (using a weak acid bath). I've done this before all right.
This time, though, in trying to put the spout back, it doesn't want to line up properly. I can't get it to point downward and be tight up against the wall. It's close, but not quite there. If I keep turning so as to point the outlet downward, it sort of jumps the threads and comes loose.

How do I get it just right, so that the spout points downward and it's firmly seated against the wall?

Thank you.

 

[Reach4]

If I keep turning so as to point the outlet downward, it sort of jumps the threads and comes loose.

Whoa... I was going to go a different way, but let's talk about that stripped-thread one as being more urgent.

When you remove the spout, what do you see? Do you see a nipple coming out of the wall, or something else?