Item frames displayed: https://i.gyazo.com/e83971a960d5da6d1d6903cb522e4704.png
Item frames disappeared: https://i.gyazo.com/9bb2487aa782604fedd48529d5e9d0f6.png
Reloading chunks does not fix: https://i.gyazo.com/64d56eabbebdafe48d490aebeddca3ad.png

I've noticed this more than once on this snapshot. When I issue a .home command that is simply a python script I wrote issuing a /tp command for me to predefined coords.

The item frames are still present, but I do not think they can be targetted directly. If i break the block the item frames reside on – both the item frame and their contents drop.

I've observed this with both items and maps in item frames.

I can find more examples of this, But the video screenshotted above is: https://www.youtube.com/watch?v=F0UXCp78Fcg