I'm running the latest version (20.0.1387.91) of Opera in Windows 8.1 Pro x64. I am frequently losing my Opera profile - in particular, configuration changes and installed extensions. I'm not entirely sure what triggers it, but it may well be linked to the installation of Opera updates.
It's incredibly frustrating, as a few times a week I need to re-download/install all of my extensions, and reconfigure my browser settings.
Current profile location according to Opera>About Opera is C:\Users[username]\AppData\Roaming\Opera Software\Opera Stable
Many of the Last Modified dates of folders and files contained in this directory are today's date, and I haven't as yet made any changes.