I've been having this weird damage glitch ever since the BT patch where I don't deal damage to bosses*.
*Not just limited to bosses, apparently. Not sure exactly when it started, either, but only started noticing with the BT patch.
Here's a video of me trying to kill Green Polpo in Commerci (Rosa):
Another video showing that it only seems to affect Righteously Indignant:
Video on normal mobs:
Up until about 0:36, I barely do anything to his HP bar. I went back and counted 44 ARs up to 0:35, and with a very conservative estimate of 600k per line, I should have dealt ~211mil damage to him (way more than twice the pre-buff HP of Polpo at 86mil). After 0:36, I fire ~21 ARs at 1mil per line (= about 168mil) to reduce him from 90+% to 0%. Incidentally, that's how much HP buffed Polpo should have).
What the heck is going on? I doubt that it's just a visual glitch since it takes me the entire time to barely kill Polpo. Pre-HP-buff, I could kill Green Polpo in < 1/4th the allotted time. The only thing I've changed with my character since the patch is obtaining the Ghost Ship Exorcist Badge, but I took that off and it didn't change anything (I couldn't even kill Polpo that time because of not dealing damage).
Probably irrelevant, but here's some screens of my equips, stats (buffed without AA or Infinity), and link skills.
P.S. It doesn't just affect me at Commerci; I think the same thing happened at Gollux (but I can't be completely sure because I was duoing).