Your quadriceps experience profile will only go up if the app estimates that you recently pushed your limits. If the exercises you do are at a difficulty level lower than your current quadriceps experience, or at a low volume, then it does not represent enough stimulus to increase your experience.

To determine whether there is an issue or not, I would need to see your detailed experience profile for the quadriceps, and the list of exercises that you did recently that you think should affect your experience and didn't. Is that something you can provide? Screenshots are fine.