Hi Juliet
Thanks for your replies and for reaching out to the Spybot team.

My computer seems to be running fine. I haven't noticed any impaired performance or negative impact.
I don't have tracking/cookies turned on for any browser.
I assume that the entries for HKU\S-1-5-21 are bad because they're picked up by spybot. In the meantime I've sent an email to what I'm guessing is Microsoft's email address to confirm if the entries are valid.