This problem has appeared after the release which changed screen locking after upload, Page not found .
A possible way to reproduce - capture a few dozens of images, start upload, enter capturing mode again.
Eventually screen is locked.
A long time ago this was also fixed back and forth, perhaps worth having some tests around this functionality 
This seems to still happen with the latest version of the app.
Still a problem in the latest app version. Have missed taking quite a lot of pictures because of this.
Still a problem in the latest release.
Still a problem in the latest release.
Noticed release notes for the latest version saying this is fixed - hooray, thank you
Will test it soon.
The problem seems to be gone, as far as I can tell.
This happened on an iPhone, so there was no SD card.