I've noticed a couple similar issues with the wolf organisation order in dens.

1. Buying wolves puts the new wolf in order of ID (I'm fairly sure it's ID rather than adult vs pup)
2. Buying wolves also sometimes seems to reorganise other wolves in your den with no clear pattern, though usually it seems like two wolves that are next to eachother switch places

These have happened to me a couple times. Recently bought Applebreeze (2820) who is older than some of my other wolves and it placed them after Little Dove and before Santiago, and afterwards I also noticed that my two full-grown progen pups, Brightcloud and Tallflame, switched places and Leafsong appeared at the end of my den despite them being the oldest of my newest litter. I don't know if these two swaps happened at the same time or when I had bought different wolves.

Oh yes, it happened to me too! After a trade with a friend I noticed that Summer and Dandelion switched places. Summer was first since her ID is lower and Dandelion second, now they're swapped and I can't reorganize them on mobile.

Edit: Aaaaand they're back in their original places, I didn't rearrange them and I didn't bought/traded a wolf like before. Weird XD

Edit 2: Nope they've switched again.

The first one happened again - Glowingsky #44035 is a pup I've recently recieved via trade through messages. They were placed between Rosanna #41037 and Crystal #44126, who are both adult WWs, which confirms my suspicion that the new wolves are placed in ID order and not age 'status'. No other wolves were repositioned.