Maybe set the priority of VTuber Plus to hight? Also make sure to install the latest graphic driver.
I've already installed the graphics drivers I used prior to the reinstall and I've tested changing the program's priority, no difference. Also changed render quality and such in the program to no avail.
Unless there's some obscure setting or driver I'm missing somewhere, this isn't making any sense...it worked perfectly fine before, so why not now?