Thank you for your help to resolve this issue which was caused by AdGuard Adblocker. I added my domain to the allowlist and the images are appearing fine now.
My apologies for wasting your time with this. Thank you for your prompt attention and assistance.
NOTE The Revibe template does not have this problem with Helix3, so there must be something in the HelixUltimate framework that is marking <img> tags that have <a href> tags as ads that are being blocked by AdGuard (and possibly others?). You may want to look into that.