Looking at the favorites Stack Exchange lists for my global account, I noticed the following questions.
For the first two questions, the number of users who added them to their favorites is 0. I wondered how that question should be one of my favorites, so I clicked on the question title to check this. The question page doesn't show I have clicked on the star, for the first two questions.
The same happens for this question.
Even though I removed some of the favorite questions, there are still questions favorite from 0 users, after 5 (or more) hours I removed them. (I posted this question after I noticed what was happening.) As far I recall, I didn't remove from the favorite questions the "0 users" ones.
I removed some favorites from the same sites of those shown with a 0. If I effectively removed those favorites without remembering it, there should be more questions showing a 0 in the first column.
I removed the questions from the favorite list by clicking on the question link and opening it in a new browser tab, clicked the star on the question page, closed the tab showing the question, and returned to the tab showing my favorites.