Yes, we got the same bug a few days ago.
We even made it to destroy all cores on his pseudo Nightmare Mode (Lasers + Rockets fromt he beginning) but then he wasn't attackable because of his shield. /sadpanda
We tryd it like 5-6 Try's, just wasn't able to kill him this day, worked perfectly on the next day.
5-6 Tyr's starting in Phase Ultra 3 ...