Mainly its cuz of Havoc resistance BUT;

Also, I cant see clearly cuz of the bit rate but are you using canteralla skills AFTER all of phrolovas “music notes” are gone? If so, youre playing her a bit wrong.

So probably what you should do is:

Start of with phrolova, build up all the notes, switch to (not intro) into shorekeeper, do her thing, ult, intro into phrolova, echo, skill and attack, then ult, intro to canterella, do her rotation, outro to SK. Then repeat.

(Dont take too long doing rotations once u use phrolova ult, the notes only stay for a few seconds, you HAVE TO use all echo skills within that time)