Problem with my list number

My watch history list says that it has 1507, while in reality it has only 1506. It's been a recurring problem since like 300th entries, and kept on going until now. I've counted entries manually, compared it with my ratings list (they're supposed to be the exact same), and even checked with some code input on inspect code browser feature:

ul li:nth-child(1506) { background-color: red; }

It highlights the 1506th entry with red background, and it does it to the latest entry to the list as I can see, so the 1507th entry is for sure not there.So the problem is that the list always displays one number higher than it actually has. I've seen that you had similar problems with other users in the past, but I would like this problem to be fixed for my account's list