I do not think this particular bug is dependent on any one driver (Intel or otherwise) as previous posters have suggested. I have also experienced this bug on a fresh installation using a Radeon 580 and the open-source amdgpu driver.
I was able to work around the problem temporarily by changing the greeter or using the CTRL+ALT+F7 key combination when I wanted to unlock the screen. Unfortunately, this problem annoyed me enough that I have since moved away from XFCE, so I am not able to perform any additional tests or provide more detailed information. I just wanted to chime in and provide what information I could about the bug.