The gloves on the core don’t seem to have an effect on Tass when he is in Archon (twilight archon…?) form. No unstoppable active and the gloves from the core went through me multiple times. First time I thought it just missed but I intentionally didn’t move out of it the next 2 gloves, and they still went through me.
Mail the replay file to the developers.
I don’t know what may have happened in your game, but I just played Tassadar with the talent in question and I was properly knocked back twice by the core.