I use an iPhone XR. My phone is always up to date. A few weeks ago the Acrobat Reader app stopped allowing me to connect to the Document Cloud. I signed out of the app and attempted to sign back in but the login screen would not open. It just sat at a spinning "processing cursor". I deleted the app from my phone and resintalled it and the same thing occured. As it is I am no longer able to access my files on the go.
I am wondering if this related to signing in from multiple computer devices with the same subscription.
Go here: https://account.adobe.com/plans ---->> Click on Manage Plans ---->> scroll down to the end of that page and see if you have more that one computer device marked as active. Remove or deactivate any device that you're not using and only leave active the computer device that you currently use.
See if you can log in again to the document cloud from your mobile device.