So, singleplayer server, -preventhibernation in the launch options, boosted stats since i'm by myself. Primal Fear being the only mod that touches creature spawns.

First time ever fighting the Demonic Reaper Queen Empress. Way out in the desert of Ragnarok so that if it went poorly it wouldn't be near my regular paths. Almost crashed the game with how many numbers there were, so i disabled hud. Beat it, got the summon token for a tamable version. Everything went great.

As it was getting knocked out by origin tranq arrow, it happened to burrow itself. So then it was invisible. I freaked out a little thinking it broke or was maybe fell through the ground. Pulled up the taming list and there she was. Yayy, got it tamed. Can see that in the tribe log too.

Told it to unbury itself. I happened to be above where it unburried, so it was a pretty cool moment rising into the air with it. Started riding it and killing stuff to see what it would do, felt really dope. Arrived back to where my other tame was waiting, dismounted, and as i was walking off the back of the Reaper Empress, she disappeared. No animation, no death notification, no death in tribe log, no movement at all; just ceased to exist. I go back to base to see if I could use the Dino Storage v2 mod's Terminal to "Admin Soul Recovery" her back to me. She's not even in the list of tames there.

I've searched everywhere and I can't find anyone with a similar issue, in modded or in vanilla, so at the very least does anyone have any idea what might have happened before I go through fighting her again, in case the same thing happens?