Looks like the old Sam and Sons Sandwich shop building suffered a major fire. Looks like the entire roof burned off and the second story is heavily damaged. It was only time for that building.
That's a shame, pretty interesting building.
Tim Gilmore just did a story about that place too.
https://jaxpsychogeo.com/2017/06/24/new-story-avon-apartments-and-sams-grocery/ (https://jaxpsychogeo.com/2017/06/24/new-story-avon-apartments-and-sams-grocery/)
most likely a transient? or electrical? but wouldn't the power be turned off in a building like that?