Hi,
if you have a sitemap with more than 40 devices present, than the app crashes. I can replicate this behavior and if needed i can also tell you the exact number of devices it takes. My guess is that most of the bad reviews in the store are due to that bug.
What openHAB version? If it is on 2.4 Please try the current testing version, 2.5 Milestone 5
2.5 is slated to be released December 15. 2.4 is almost a year old and there have been a multitude of changes since that release.
If it is indeed a bug in Milestone 5, you need to open an issue on GitHub. Many of the developers do not use this community forum.
That seams to have fixed it. Thank you very much!