The 11.8.2 beta is now ready, if you'd like to give it a try.
You'll need to set a registry entry to test things (see the last line of the release notes). Please set that as described, and let us know if you still see the slow folder reading. If it seems to have fixed things, please delete the registry setting just to confirm that things return to being slow again, in case it was just a coincidence. (Of course, you can then set it again to keep things fast, and based on your feedback we'll implement a more permanent fix.)