First time this has happened to me, I hit the defend button and went to fight an opponent, and they made the first move instead of me. Not a huge problem since I have a good team that won the match, but has this happened to anyone else where the AI gets the first turn?
Yes.
It’s quite rare, but it has happened to me a few times.
Maybe once every 50-100 battles or so?
It happens. As Stix said, it is rare.
To me it has happened twice this year.
Problem already presented to Support here:
(By the way, this is in the wrong subforum, since it’s a bug issue and not actual gameplay chat.)
(You could have just moved the thread, you know 
For some reason the two of us can do that)
That is true, but I forgot. 
Which category should I place it under? The choices are: uncategorized, game play chat, featured request, guilds, support, community guides, and off topic. My first thought would be the support, but I don’t need support, just wondered what was going on with the AI turns.
Yes, it’s in Support since it’s a bug issue. Mel moved it for you already. 
I just dump all my threats in whatever the default is. Crowded then ends up moving them to whereever he thinks is most appropriate