When I run my Today Extension on the simulator everything works fine and it displays the following as expected:
I had an issue using custom ViewController in my Share Extension. It turns out that the resources are limited in Extension mini-apps, so when my Extension was generating thumbnails, it crashed the extension because too many background threads were being used. Reducing thumbnail generation to a single one at a time fixed the issue.
The confusing part was that this limitation was not seen in Simulator, only on a real device.
The sources of my problems:
hope this helps someone