I just ran into this very frustrating issue using the password generator. If I open a new password generator window and increase any of the settings (length, digits, symbols) I cannot then decrease any of the settings. The sliders act "stuck" and swiping left only serves to open the "words" menu. I was in a hurry to generate a password and this drove me crazy. I found later that if I cancel that password and then reopen the generator (clicking on "+" to add a new password) the sliders work (more or less, the first attempt to slide left causes the screen to slide down so your finger moves off of the slider; however the value is decreased and the generated password changes accordingly). Version 6.4.1 on iOS 9.3.2.
I would classify this as a bug as it is repeatable (for me at least).
1Password Version: 6.2.1
Extension Version: 4.5.5
OS Version: 10.11.4
Sync Type: iCloud