So when I browse the map for the server I'm playing on a strange 'shadow' appears and blocks my view of whatever the 'camera' is pointing at. No idea why. I'm using the Brave browser.

BlueMap 3.14 on a Windows based Vanilla server

Not a bug, see: https://bluemap.bluecolored.de/wiki/FAQ.html#q-my-map-disappears-when-i-zoom-in ("My map disappears when I zoom in!")
If you have more questions about this, please visit us on our discord :)