Gallery not showing photos

[Sy777370]

Gallery is only showing blank frames, not the photos, in folders with many photos, 750 and more. It does show photos in folders with smaller numbers. Photos are in subfolders of DCIM folder on SD card. Google's Photos also has this issue. Phone is an Android Moto G Play.

[Sy777370]

This updates my issue above. After rebooting several times I was able to open the SD Card DCIM subfolder with the most photos (~4k) and then by scrolling down slowly the photos eventually loaded. But another DCIM subfolder with less photos (~750) also has this problem and only shows a portion of the photos, most are black with exclamation points in yellow triangles. When I click on one of these it says "Failed to Load Media". Scrolling down does not help.