I'm not sure what's going on, but .heic photos seem to change to .jpeg format in certain situations. I was under the impression that .heic was able to retain more information and data than .jpeg.
Here are situations in which you'll find your .heic photos transforming into .jpeg:
1) editing photos within Apple's own Photos app
2) plucking choice photos from burst shots
3) photos were taken while filming video
4) sharing front camera photos between devices that are compatible with .heic (8's and X's)
Mind you, I've never change to .jpeg (most compatible) in the settings. All my format settings are default for "high efficiency". Video was shot at 4K 60fps.
Here are situations in which you'll find your .heic photos transforming into .jpeg:
1) editing photos within Apple's own Photos app
2) plucking choice photos from burst shots
3) photos were taken while filming video
4) sharing front camera photos between devices that are compatible with .heic (8's and X's)
Mind you, I've never change to .jpeg (most compatible) in the settings. All my format settings are default for "high efficiency". Video was shot at 4K 60fps.