Welcome! Hopefully you'll find the answers you need here.
I agree it looks like a burn. You need to figure out how it happened and make sure it can't happen again. Can you post a picture of your enclosure? Maybe someone here can see a problem you missed.
To post a picture from your computer, use the POST REPLY button (not the Quick Reply Box). Click on the paperclip icon, follow the instructions to upload the picture from your computer.