This worked for me:
On Pioneer receivers, you unplug the unit, fully powering it down.
Plug it back in, but do not power it up yet.
On the front panel, find the button marked “Enter”. Depending on unit, this may be a single isolated button or a bar type button along a line of such bars.
Press in the Enter button and while holding that depressed, push the ON power button. Hold these in for several seconds, then release the Enter button.
You should see the “Reset [Yes]” type question. You can toggle between Yes and No with front panel Up and Down buttons. With Yes showing, press the Enter button to reset the entire receiver.
This clears errors in the HDMI, and also any other setting errors that you may have.
Best of luck —- Michael