Something of note and I'm not sure it's been mentioned though I have tried to peruse a lot of the support to see if there are definitive fixes yet. I know that Sega and Microsoft players are looking at this and hope there will be swift resolve. What I wanted to note though is that the game itself looks like it is being only installed temporarily on some Windows systems. What I have experienced is a little hit and miss. So for me it has been a situation where I get into game and can play no problem. I then can hop out of it for a bit maybe 1/2 and hour or so and go directly back into it. But say I am doing something like watching a movie or browsing Youtube... once i come back to PSO2, it does not prompt for UAC or load. Which makes me think that the temporary installation of game files had been purged as it was only cached instead of actually installed on the hard drive.
In the picture that I linked above, it shows there is a blank space/greyed out space where the PSO2 app is running. Now this type of behavior at least that I am having is related to the installation of the game being placed in the wrong area or possibly somewhere temporary. I can't name off the games that I have played that have done this, but I remember distinctly this situation at least 3 times with 3 different games.
Another reason I feel there is something wrong with the installation process showing temporary is that after some time where I've stepped away ...I try to play it and it doesn't launch but it looks as if it's all there. Then, you look at the properties of the system where it only recognizes as 11GB instead of the whole installation of the game being around the 80gb. Even in my Programs and Features it was only showing 36GB. At this point, I have issues trying to remove it and have to run the uninstall and reset and just let it sit and then reboot after like 20 minutes to make the files release and uninstall. Then fiddling with it more and after a reboot, it works again. Installs and pops up the PSO2 splash screen...installing the game files and waiting for the "START GAME" button to be pressed.
So again I know that this might not be for everyone but this is the experience I've noticed and figured to note it just in case the devs/support need it as data.
Hopefully there will be quick resolve....take care and be safe.