Unfortunately this is a known problem with the A13 update, due to a change in Android security rules. Please see posts above in this thread, and please read here
and see here for a wiki-list of apps that are affected or that aren’t (maybe you will be able to contribute):
For your roaming problems I would recommend getting in touch with both Fairphone official support (click > contactsupport for more info) and also contact your mobile network operator, even if the SIM works for roaming in a different phone. This is complex territory and both “sides” need to know about the problem.
For the blank screen, some users have found that this stops happening when they disable automatic screen rotation (go to Settings > Display > Auto rotate screen).
See this and following posts: