Not sure if this is a bug or not

I tamed a wolf in the overworld (red collar) and named him with a name tag, then I took him into the nether to fight skeletons

After he was injured I went back through the portal to the overworld to get meat, my wolf stayed in the nether, I didn't tell him to sit - but when I got back into nether the wolf was completely gone, I walked around hoping it would teleport to me, but it never did, it also didn't reappear in the overworld and I'm pretty sure it has despawned

Any ideas on what happened?

UPDATE: After saving and exit, and then re-joining, upon going into nether and going higher up in the world the wolf has teleported to me. Perhaps he teleported above lava lake level when I left the nether, as our current build level is below the lava sea at level 5-6? Or as chunks were reloaded it realised he should have been present? Not sure, but I'll add the info if it helps any