It's a visual buffer corruption issue which is meant to be fixed in the later betas. As I'm behind in getting the issues with what's been reported against the build from wednesday, it's going to be a few more days before you'll get access to a beta build.
So I would kindly request holding off reporting issues until you've got access to the newer build as most of these preview build issues that you've noted have long since been resolved & for those that haven't then it's better to revalidate them against the current code base vs the one from 5 months previously.
-dro
