Why is my state tax refund amount showing up as $0 when it said my credit should be $534? I always get a state tax refund. Is it a glitch? I've never had this happen.

Have you reviewed the actual state tax return to ensure the information properly populated from the federal tax return? 

If you already e-filed your federal tax return and clicked on to amend it, it will clear the refund amount on the tax home screen for both federal and state refunds.

Which specific $534 state credit?   PA has very few of these.  And some credits are nonrefundable.

Deductions and Credits (pa.gov)