Safari: Collapsing Layout of Simple Masonry – SiteOrigin Widget Bundle

I’m experiencing an issue with the SiteOrigin Widget Bundle Simple Masonry in Safari. The Layout of the Grid is collapsing for no reason. When I load the page the first time (after starting safari) it is displayed correctly (most of the time, not always) but everytime I refresh the page or click any link the layout of simple masonry grid-items breaks. The page can be forced to display the grid correctly, when I cmd-open a grid-item in a new tab. I can recreate this issue across several mac machines and different Version of OS and Safari. I’m using SO-WB with SO-PB

Things I tried so far without success:
Setting Height 100% !important for its container.
Setting a fixed width (px) for its container.
Disabling the border.

Here’s some screenshots. I’d be happy to give you access to the site if you need it. :) Help would be much appreciated.

Safari:

Chrome, Opera, Firefox, IE: