I am seeing weird triangles in the editor

Let me check...

go to the console, and see if there's any errors.

Probably a weird browser render problem.

i am also experiencing this issue, and reloading the tab / logging in and our isn't solving it...

Welcome to snap! where you on flat mode?

i have no clue what that is...

the white mode of snap

Settings > Flat design
image
It's Snap! light mode.