If your app is freezing or crashing, whether during login, when importing or during the signing process, please try clearing the application cache from the device settings. A screen recording showing the clearing of cache is attached with this help article. 

If it is still an issue after clearing the cache, please reinstall the app. Sometimes an update might go bad, or some corrupt data might cause issues. A clean install will usually clear the issue. Your settings and documents will be saved even if you reinstall.