Hard to say; but at about 18% my guess is that it's probably sticking on something in Edge or Edge Chromium, possibly something in Internet Explorer.
Do you use one or more of those browsers?
But those should be on the OS disk which should be 'awake' anyway.
Do you have anything that would normally be on the OS disc redirected to another disc?
As it's only 'sometimes' then it makes it harder to track down. (It always does with intermittent issues).
It may be that something CCleaner is trying to clean is on an inactive disc, that would depend just what is on them and how you use them.
It may be that something is ocassionally running in the background when you run Health Check, and Health Check can't close or handle it?
(If it was happening everytime then it would indicate maybe a browser, or something else, pre-loading and running in the background).
One thing that often helps if CCleaner is 'sticking' is to do a run with the Windows built in Disk Clean-up.
It takes a lot longer that CCleaner but can sometimes clear jams that CC can't.
I don't think it would help here, but it can't hurt and it's a good idea to do one occassionally anyway. (I do one about monthly).
I'm assuming that you don't have all sub-categories for those 3 Windows browsers ticked in Custom Clean?
If so then one of the unticked catagories could be what Health Check is getting stuck on.
Something to try straight after Health Check has frozen, so you know that the problem exists at that time.
Close the frozen health check, relaunch CCleaner, and switch to Custom Clean.
Try right-clicking each unticked category in turn and selecting analyze (not clean) from the popup menu.
If the analyze baulks at one of them then that indicates the culprit.
You could also try that for any other unticked items in Custom Clean.
TBH regular (long time) users prefer to use Custom Clean anyway - it gives more control over just what is and isn't cleaned.
It doesn't automatically run the 'Software Updater' or 'Startup' tools each time, but you can easily run those manually from the Tools menu if/when you want to.
To set Custom Clean as the default go to Options>Settings and change 'CCleaner Home Screen' to 'Custom Clean'.