Getting sporadic booting directly to Powerpoint application

I'm unable to duplicate this behavior on demand, but it is happening about once a week now. I do a normal Shutdown every night, and the next day it will either boot up to the desktop, or it will boot up directly into PowerPoint. My husband uses PowerPoint extensively as a college prof and I'm scared to pieces that something will go even more wrong and it will lose his data. I do have restore points on, but wouldn't know which one to select and kind of assume the problem will come with it. I'm thinking I may have to delete the app and re-install it. It's the only thing I can think of, but am very concerned about the data, and wonder if it's even a PP problem, since it happens when the OS starts. I'd appreciate any advice on what to do (and bear in mind I'm just a regular user, not a tech)

I'm using Windows 10 with the Creator's version. I get updates automatically for fixes. I have an HP Envy 700. I have Norton-always on and Malwarbytes-only run on-demand. No problems found. I have PowerPoint 2016.

Thanks!

I had no idea the functionality changed. I hate updates. Anyway, I appreciate the help. I'll consider this closed if the behavior stops. Have a joyful day.