Gym defender couldn't come back

I went thru this too. Eventually it did come back. The next time i took the gym i got my defender back right away however the gym still had a defender icon on my badge screen. I was unable to check and see if it counts towards your 20 gym limit but would like to know.

I had this happen to me once as well. I tried reloading/reinstalling the app, which didn't work. I've had some people tell me that physically visiting (and clicking on) the gym you were knocked out of can fix the issue, but since this was on a gym fairly far out, I wasn't able to do that either. After 2-3 days, my Mon finally came back to me. Fortunately, this issue seems to be a very infrequent occurrence.