I have been having this issue of 100% disc for about 6 months - I have Dell Pro Support. In the end, they sent me a new Laptop to replace the other laptop I bought 6 months prior. The new laptop starting doing the same thing - 100% disc, but also the computer was having random critical errors saying loss of power or crash (Kernal error 41 Cat 63). My routine was to put the computer to sleep and then when I would come back and open the lid, and check the event viewer, there would be the Critical error showing up that something happened while it was asleep. We went through every troubleshooting option we could, different techs, check disc, etc. Turning off fast start up in power options, resetting power plan, disabling superfetch, updating Bios and drivers, etc... You name it, we did it. So they just replaced the motherboard and same issue. It would hang at 100% disc for 15 minutes or longer when starting the computer.
After a little research on my own, searching WaasMedic Agent Exe and found that Dell Support assist could be the culprit. It showed as WaasMedic on the processes tab of the Task Manager, but on the Details tab, the disc hog was DSAPI.exe. Googled that and it was in fact reported to be Dell Support Assist. I went to the control panel, programs, and uninstalled Dell Support Assist. (I still have Dell Command Update) which works fine. After uninstalling, the 100% usage immediately stopped. I restarted the system multiple times to see if it has resolved on restart and it did. No more 100% disc.
I then went back in and re-enabled the Fast start up in the power plan and restarted and still resolved with no 100% disc.
I also checked the event viewer after all this and sure enough, the Critical error (Kernal 41 was created at the time that Dell Support Assist was at 100% disc, along with another error (Windows Remediation of some sort).
Dell support assist can easily be reinstalled if I were to need it temporarily so I'm leaving it off.
I also found this article when trying to figure out why I was missing power options in my plan. https://superuser.com/questions/1536904/windows-10-power-options-missing-on-new-laptop
Turns out the new systems use something called connected standby so processes continue to run when your computer is asleep. These reg edits described might solve not only something happening when the computer is asleep, but look to also provide a way to return all my missing power options.