I think some of the mega hits are not hitting. (possible bug?)

I had my mega Ray hit the raid boss a few times, the rainbow colour gone but the shield not broken. when I went out the lobby healed it and hit it again, the last shield fell.
In another case the shields were not at all reduced(7/10 still standing) when like 12 people who I frequently raid with raided, we all had to heal and hit again. is it possible it's a bug?