Same issue here, on all PCs in the office.
Wiping the cache helps for couple seconds only. If we then open 3-4 images, issue repeats again.
Workaround is to click to see another conversation, then come back to the original conversation, and try to open the image again fullscreen.
We may have to repeat the workaround 4, 5, 6 times before we finally see the picture.
Disabling GPU hardware acceleration does not help.
Other workaround is to see images on our cellphones, as Android is not affected by this issue.
Issue has been persistent for over a year. Much frustrating for all users in office.