After a restart of my iOS device, an iPhone in this case:
1) Open an app that requires credentials from 1P.
2) Tap "Passwords" to launch 1P. (1P is configured to allow TouchID and Lock on Exit.)
3) Use the Master Password to open 1P for the first time since device restart.
4) Tap credentials and proceed as expected.
5) Some time later need credentials again (same app or another one, doesn't matter).
6) Tap "Passwords" to launch 1P.
7) Expect TouchID option to be available to unlock 1P, but it is not. TouchID does not become available until I explicitly open the 1P app and unlock it with the Master Password.
I usually remember to open 1P explicitly after a restart of my iOS device -- but sometimes I forget and run into this issue, and it's very annoying.
FWIW -- the macOS 1P app does not appear to be subject to this same problem.
1Password Version: 7.3.5
Extension Version: Not Provided
OS Version: iOS 12.4
Sync Type: Not Provided