De spawned at dawn I suspect. You started taming them at night?
If you’re taming night spawn wolves you have to start early or they will de spawn at sun up.
I’ve successfully tamed night spawns but you have to stay within visual distance at all times and then breed a pair of night spawns which creates a proper spawn cub.
The cub will then act like any day siawned wolf.

So essentially. Tame one night spawn. Fence them off. Bring another nearby and tame. Then breed them to create fully normal wolf that won’t de spawn