I have created several mastery paths. I have also had to fix others teachers mastery paths. Is there a way to automatically send assignments to a mastery without going in to every assignment and either clicking the box or assigning it to mastery paths? Some teachers have several assignments within a mastery path. Assigning everything to a mastery path becomes very tedious work. I would think a one-click option would be a good feature.
I was able to look around on this for a few minutes. It looks like there is not a faster way to do this unfortunately. Currently the assignments that you want to assign to Mastery paths have to be done one by one. I do agree that this can be tedious, especially with large courses that contain a lot of assignments for the students to complete. THIS is the official guide for assigning conditional assignments to students for Mastery paths.
This might make a great feature request for future releases in Canvas for Mastery paths. Not sure if you have time, but you could always submit an idea for improving this function HERE.
Hopefully this helps! Sorry for the inconvenience on that.