Jarven's Martial Cadence not proccing

In my last match as of writing this I was playing Jarven the 4th. I noticed that every time I went to attack a new target he would stop all animation for about a half second then start auto attacking. I looked at the damage numbers and notice that his passive Martial Cadence never actually went off. There was no animation and no damage. I don't have footage of it sadly since I wasn't recording the match.