Thats correct, we use it when there are issues rendering with the GPU. What i'll do is move this thread over to the Beta forums now, so it's seen by the Dev team and anyone else using the Beta
I've been able to replicate the issue, it didn't happen straight away but after a minute they disappeared. Closing and reopening the file, they came back but went again after a minute.
Can you just check under Edit>Preferences>Performance and what is the Renderer set to? Can you try setting it to warp and seeing if this happens again.
Also i've just noticed you are using the Beta, in future, please post all issue found with the Beta in the Beta forums here
