took some pics using LR's DNG with my iPhone today. they did not show up in LR or on my phone anywhere. turned the format to jpeg and suddenly no prob. what gives? took some really great pics and now I can't find them anywhere!
I'd like to ask some questions, share some suggestions...
What model iPhone do you have? What iOS version is running?
How much free space do you have left on your device?
Does it help if you quit LR and launch it again?
Do you have many apps running? Does it help if you quit all other apps?
Does it help if you restart the device?
...All these questions are essentially about clearing device memory to make more resources available to LR.
If none of the steps above help, I'd like to suggest you please try making a full iTunes/iCloud backup of your phone. Then Restore that backup onto your device. It may sound strange, but I have seen this help with similar troubles. My guess is this may smooth out file system issues which might cause performance or file write trouble. Though this effort takes time, it cannot hurt to try.