It's set to show in Self Service, but is it actually scoped to any computers? Is it set to "Specific Users" with no limitations/exclusions, or is it set to All Computers?

I have several policies scoped to All Computers. No limitations/exclusions. Also, verified policy is enabled.

Was is the recurrence of the policy? (Set in the General tab.)

Recurring check-in, and the execution frequency was set to Once per Day. I have since changed that over to Ongoing and everything seems good on the machines now.

Great! Good catch.

Thanks for your help emilykausalik!