Media File Missing?

FM 5.6.13 Photos 4.0 OSX 10.14.6
Random, and numerous, photos within my Photos library within the FM Image Browser have a red exclamation mark saying “Media File Missing” and the sub-text says the file is missing, it may have been deleted, removed or renamed. The image is still sitting there in Photos, as it has always been, and displays normally within Photos app.

There seems to be no order or logic to which photos are showing this.

Reboot of Mac, Photos, FM - no effect whatever.

I am aware that there are several previous posts referring to this issue - I’m just adding my experience to the list.