iPhone email - no image in signature/blue question mark intead

In the last 24 hour, the image in my email signature suddenly disappeared and was replaced with a blue question mark. I am running with the most up to date iOS (17+); the signature was created via Email Signature Rescue. The box with question mark is, in fact, hyperlinked - and that still works. No issue with iPad. And, emails sent from iPhone show image on other devices. Reset settings to no avail (though frustrating); and restarted many times.