Hello iomob,
your issue is pretty interesting. The problem probably resides in the fact that you are using an implicit authorization flow, so you do not get the refresh token.
My solution thus is enable authorization grant flow, and once having the refresh token just schedule the session refresh to be repeated every hour. With the amazon-cognito-identity sdk for Ionic, this is easy.
If you want I can send you my apk.
Please, message me at anytime to further discuss.
Simone
PS: to see the idea of the solution, read the github issue (where I participated) that solves the problem [login to view URL]