That is possible.
The deduction lowers your taxable income.
If your tax liability zero's out, the deduction won't lower it anymore.
If you get credits, that is added after the tax liability is computed, so you could be getting a refund, but the refund does not increase when the added deduction is entered.
Please view your 1040 and look at lines 12b for the 600 CARES ACT deduction, then line 24 to see your tax liability. Perhaps that 600 less taxable income made no impact.
To view 1040
Click TAX TOOLS on the left side-bar
Click TOOLS on the drop-down
Click "View Tax Summary" on the Tools Center Screen
Click "View 1040" which now appears on the left side-bar