If you are using Checkvistle, we can hardly help with the bugfix as is not our app, it is developed by a third party using Checkvist's API.
On the other hand, Checkvist has its own mobile webapp that works offline - https://m.checkvist.com
If the login problems happen on the mobile webapp (m.checkvist.com) we will research the problem and definitely help :)

Hello, are you talking about https://m.checkvist.com - this is URL of our mobile app. Can you open it?