The tool tip area under where it says Minecraft shows the icons (randomly placed) of the the contents inside a Shulker Box.
I even tested it with loading a brand new instance of the modpack (1.3.5) and the bug(?) still occurs.
Here's the image:

looks like bundles plus is rendering the bundles view for shulker boxes too. might be able to turn it off in the config

Turning off the tooltips in the config file seems to have fixed the issue!
Thank you.