When flying around in creative mode on a new world and loading new chunks, I could see passive mobs in chunks that were loading (the blocks had not yet loaded). I first noticed horses in a loading chunk that died. I flew down to the location the horses died and there were no drops (which is not necessarily odd since horses sometimes drop no items) and then while continuing to fly I noticed the same thing happened to cows, which did not drop and beef. There were no blocks in the eventually loaded chunks that should have caused suffocation damage.

It's also worth noting that many of the passive mobs did survive, but I did observe this issue on a few "packs" of passive mobs

What I expected to happen was...:
Passive mobs to survive while chunks are loading

What actually happened was...:
Passive mobs died and dropped no items while chunks were loading (see above for more detailed report)

Steps to Reproduce:
Fly around on creative mode in new world and load new chunks