Hey @Norm I have a Div with visibility set to none, and I have a button that is set to trigger visibility for it. If the Div has flex set, it is visible on the initial page load. Toggling the visibility works, just not the initial load.
This was working fine in 4.4.
EDIT: Fixed it by adding !important to the display:none on the .object-hidden class. Interesting this was not an issue with the stable build.
I have never seen this with another app on my Mac, including Blocs 3, however I cannot think of any others that provide progress animations in the dock during use and I suspect that is at the root of this.