How I can stop my navigation bar from blinking

My site is based on the Flask tutorial and I'm having a problem that I don't see anyone else mentioning. After my site loads, the left half of the navigation bar "blinks" (disappears and then reappears) very quickly after the user clicks begins interacting with the site. This started right after I finished the tutorial and it's still happening today. Can someone explains what is causing this and how I can stop it? It happens with Chrome but it never in Firefox. Here's the site:

Hmm, I've not seen that happen before. I just checked out the site using Chrome (Version 60.0.3112.101 on Linux 64-bit) and didn't see anything like what you describe. Which version of Chrome are you using? Which OS?

I'm using Chrome Version 61.0.3163.100 (Official Build) (64-bit) on both Windows 7 and Windows 10 and see the blinking. I tested it on a Mac and there was no blinking.

I've just upgraded my own Chrome to Version 61.0.3163.100 (Official Build) (64-bit), still on Linux, and it's not blinking. Maybe it's a bug in renderer in the Windows version?

It seems like it. Do you have any idea how I could diagnose and fix the problem?

i'm not sure... maybe you could report a bug against the bootstrap project, or see if they have any similar-sounding bugs there?