Not sure if we're talking about the same procedure - don't try to add the device back to Geo-Filter/Traffic Prioritization. Just connect the device back to the router - it must be connected via ethernet/2.4/5GHz whichever method it was connected before. In the Device Manager it then must be named the same as it was previously and given the same device type. Then once that's all done the error should go away.
100% though a factory reset will clear it otherwise, hold the reset button for 30 seconds, then wait 2 minutes before accessing the interface and it should be fine.
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