Not an answer, but I have experienced exactly the same thing and this has now been going on for months. For me it takes around 7-8 minutes. The sound sets are installed on a removable USB3 hard drive. It hangs there on the line: 'Scanning Sound Sets...', but interestingly this only happens when first running the software after a computer boot-up, or restart.
If I just closed the software or a song and started another, or if I close Studio One completely, but don't reboot the computer, then this step only takes a few seconds.
I would like to know what would change if I installed an M.2 SSD on my laptop and then moved the Studio One sound sets to that?