King in the Mists untargetable during 2nd phase

Finished the 1st phase of the boss fight in the upper area of the arena, with the boss standing right above the wooden ramp; it took longer than usual for the phase transition, and when I got back in the arena the boss wasn't damageable in any way.

It spawned right at the feet of the opposite ramp of the same construct (moving from north to west of the arena), outside of the invisible wall blocking access to the ramp, with one foot inside the non accessible area.
It would only start doing any attack animation if I got in between it and the western edge of the arena; I could not get behind him and stand in between him and the invis wall.

Logging out and back in did not solve the problem.

https://imgur.com/a/welp-MytmR1K

I had exactly same bug today and same position.