Hi John,
I have a similar question. Images in our organization's SharePoint are taking long to open or are blurry.
We recently migrated to SharePoint from an on-premise server about a month ago. This lag was not happening before the migration.
My coworker uploads photos to her computer, moves them to SharePoint site on her desktop, and anywhere from 24-48 hours later she tries to view the photos by scrolling through in Photos. The images take anywhere from 5 to 60+ seconds to load, a bit faster when she is viewing the photos on SharePoint Online but there is still a lag. Sometimes as she is scrolling, she gets kicked back to the first photo in the folder. These are high-resolution images and some are large in file size. There is no concern with storage space on our organization's SharePoint.
We have tried making the files "always available on this device" and there is still a lag. This adds unnecessary wait time when she is quickly trying to view photos. Thanks for any insight you have.