I'm also having this issue.
I'm a new Opera user (within the past month), so I can't really say whether or not it's an update that's causing it.
- Opera - 53.0.2907.37
- Windows 10 Pro - Version 1803
I did recently update from Windows version 1709 to 1803. I'm not 100% sure, but it feels like a new issue that I didn't see on the previous version. I know Microsoft made a lot of changes as far as graphics and scaling go, so perhaps that could be a source.