edit; predictable, server is stuck trying to rebooting (Please wait for system event notification service). I'll wait here for a bit.
You can always stop the core service through MS services and wait for the service to finish. Even if it times out, it'll finish ... eventually. To the original issue, especially if you never ran it, the Checksum check will take a long time to run. Then it depends on size, speed of disks, and core resources as to how fast that first pass will take. However it will have to finish otherwise it'll just keep doing that over and over and over, unless you turn it off. It is just a big job, especially at first. The RPFS jobs run in the back ground whenever they can and/or whenever the files they need to purge are not locked. So they fact the just picked up and ran is normal. Generally I'd suggest to not cancel the RPFS jobs, stopping the core service is one thing and letting RR shut itself down, cancelling any database from deleting data however, I wouldn't recommend doing for any vendor personally.