Since commit https://github.com/xfce-mirror/xfwm4/commit/940cfef1c7b5828b951b392b75baecc1638619be I'm unable to see anything when compositor is enabled - screen is not refreshed. It works on intel machines, but doesn't work with my nvidia GPU (proprietary drivers).
Well, it just means present support is broken on your system... I am not willing to install NVidia proprietary driver, so you're on your own there, I'm afraid (unless you can pinpoint a bug in xfwm4 present support and provide a patch).
XPresentPixmap fails, generates an error (in "present_error_handler()"), but "myDisplayGetScreenFromOutput()" returns NULL, so XPresent isn't disabled. In case of error, WM should shutdown XPresent for screen and fallback to GLX. Or maybe there is another bug which causes that "XPresentPixmap" fails?
OK, if we get an error then it's a good thing, we can work from there. As for XPresentPixmap() failing, that sounds like bug 13257, are you using a 32bit or 64bit hardware/OS?
64-bit OS, Manjaro unstable branch (almost Arch Linux), nvidia drivers: 375.66