Published Projects load but have missing elements.

Hello,

I have a few Developers recently tell me or question me about what is correct in my mockups. Three developers looking at the same prototype link have had different viewing experiences and also noticed some resize anomalies.  The resizing seems to show that when they adjust the browser window, some elements seem to disappear. For example, the left panel goes from white to either disappearing or changing to a gray background.  See the animated gif.  As they work and move/resize windows around, this left them wondering which is correct for the UI and if I was even aware that it was changing like this.  I told them I wasn't aware and so I'm filing a BUG.

It's a project I've been working on for a bit that has an established SHARE LINK. I typically review the link before I share it with any Developers to make sure it matches my local preview.  It looked good, so I dropped the link into a Jira story for them to work from.  Some are on Window, Linux, and Mac and all typically using Chrome browser.   The Dev who reported it to me sent me the link he was working from so I could double check that it was the latest and I even republished and it looks fine on my machine.  Still looks or behaves oddly on their machines.

Is there a cache issue?  Refreshed the browser and also tried loading in INCOGNITO and still have the issue on their machines.