I know this is not your issue but Tutanota is not working correctly with 1Password and Autofill (I imagine it's not working with any autofill). Basically, it appears that the password is being appended to the text field hint rather than replacing it. So you end up with the word "password" followed by your actual password. The developers and the open source community around the project don't seem to know how to fix this. If one of your developers could point them in the right direction it would be great and would help out any of your users trying to use their app.
Here is their GitHub issue on the problem:
Thanks in advance
1Password Version: 7.2.7
Extension Version: Not Provided
OS Version: iOS 12.1.3
Sync Type: Not Provided