Exposure problem

The 1 second max exposure in Pro Mode has been in place a long time for the Lr iOS in-app camera.  I am less familiar with the Android app, and can't speak to feature/change history.

Mobile camera sensors have improved much since the early days, but still pale compared to more advanced cameras.  In low light, some modern smart phones can capture amazing long exposure images.  What's not obvious is how much processing the OS applies to those images to reduce noise and clarify the image, and the platforms do not always make their "secret sauce" available via public APIs for apps like Lr to utilize. 

It's an interesting suggestion to ask LR Mobile to bring back long exposure for dark scenes or night sky, etc., where merging frames is geared towards increasing apparent exposure.  If this interests you, I recommend writing up a new post in our Ideas section of the Lr forums.  Please describe what you are trying to capture, how long exposure would help.