Maria let me know today, 10/1.
When editing Featured Tiles' Summary box, they are trying to add links to bullet points. Sometimes when adding a link in the WYSIWYG editor, it flashes so you can't click on it. It's not consistent, but it happens on Chrome, Firefox, and Safari, but not consistently. Only happens in WYSIWYG editors, not Gutenberg.
We've had this issue on other sites, but not sure if we figured it out or just ignored it. Developers may be unaware of this issue because they don't add content to WYSIWYGs very often and content people may ignore it because it is an issue that cannot be replicated and seems to be random.
https://wordpress.org/support/topic/visual-editor-flashing-insert-edit-link-popup/
I added the possible solution to the editor style sheet. Perhaps that will do the trick.
.mce-tooltip {
display:none;
}