What @Ashpool suggested seems to have worked for me. In case anyone is interested, here's what I did...
First, with the RP up and running and the TV screen displaying correctly, I queried for the HDMI mode used:
$ tvservice -s
state 0xa [HDMI CEA (16) RGB lim 16:9], 1920x1080 @ 60.00Hz, progressive
From this and the RetroPie documentation on HDMI Mode I learned that in /boot/config.txt I had to set
hdmi_group=1
(for CEA) and
hdmi_mode=16
(for 1080p at 60Hz and 16:9). I also had to add
hdmi_force_hotplug=1
After rebooting the RP, the issue was resolved.
Thanks again, @Ashpool!