Upon finishing my AI degree, I was left with the empty feeling of pushing myself to learn more. Not talking the dynamic of going onto a masters degree. More the dynamics of learning more mathematics and more about programming.
It can be difficult to challenge yourself when you have gained a good set of skills from university.
Finding problems online, in books etc... becomes an immense challenge. You can find problems, but they are either too easy or too hard. You can find problems that are just right, but they are not interesting. I try and buy a lot of books where I can I find some of these definitely for mathematics anyway have a lot of interesting problems you do not find so easily online.