Vastweld colossal guardian becoming untargetable

There are a few other posts like this, but I couldn't find any that posted any more complete information. Shortly (possibly immediately?) after Vastweld moved for the first time (he rotated clockwise), he became untargetable. I had a totem which worked before he moved and after didn't, and no attack I performed would affect the boss. After some time waiting, he did not appear to do the moving attack again either, but I gave up and quit hoping I wouldn't have to die to escape the fight.

Bug id: 3,146,599,408