Ho @Anthony_Del_Balsoa and thanks fo reaching out!
This is actually an expected behaviour, the Today and Upcoming Sections do not support sorting; so they’re not available when you sort your My Task list by due date or projects. We have a #productfeedback thread on this topic, so if you haven’t yet add your vote by clicking on the “Vote” button at the top of this thread 
Sort tasks by Due Date WITHIN Sections
Hope this helps!