Unless I have missed something, it looks like Canvas may be lacking in a particular feature that would make a big difference.

I suggest adding a 'Project' mode alongside the 'Quiz' and 'Assignment" modes. How would these differ?

The Project mode would allow students making individual projects, or assignments that are complex and take a long time to complete, to work in the submission window, then save and log out. Later they can return and continue working up until the due date.

Currently what happens in 'assignment' mode is that there is an autosave function that the user has no control over. So long as the student does not hit 'submit', and waits long enough for autosave to refresh, then he can leave and return to continue later. But if autosave did not kick in, then the latest added material is lost. There needs to be more student control over this.

Another current work-around is for the teacher to allow multiple (infinite) submissions in an assignment, and the student submits every time. Now the student cannot edit the submission at a later time. But if the student goes to 'submission details', opens the latest submission, selects the whole project so far, including all text, math equation entries and uploaded pictures without missing anything, then the student can paste all of that into a new submission box and continue working.

Neither of these is great, and includes the risk of data loss and wasted time. In the 'Project' mode, the intent and expectation is that the student can work for a while, click 'save' without submitting, and return later. Even better would be a warning if the student closes the program in project mode: "Do you want to save your work first?"

Another option is simply to add this feature as an option for designing quizzes and assignments.