I just stumbled upon the following. I had an entry in my vault that only has a password and an URL. As there should be a username too, I tried to edit the entry in the Android Beta App and add a username. When tapping "save" the error message "No Change" pops up and the entry ends up without a username as before. I could repeat this behavior on another entry.
Then I added the username on my Mac in the Chrome Browser extension of 1Password which worked as designed. Then I deleted the username in this entry again (in the Chrome Browser Extension). Went back to the app and added the username there again, which then worked fine.
The "No Change" error message only seems to pop up when you try to change older entries in the vault.
Not sure if you are already aware of this.
1Password Version: 6.7.2.BETA-1
Extension Version: 188.8.131.52
OS Version: Android 8.1.0
Sync Type: Dropbox