Exporting a transparent PNG produces a black background.

I don't know what is going on. I've created many transparent PNG's using Illustrator, but today nearly every attempt has resulted in the final image having a solid black background instead of transparent.

I export selection, check the cog and transparency is turned on. Out of curiosity I repeated the process but selected White in the cog and it still saved a black background.

I've created new projectd, made the most basic shape, and after exporting, the same thing happens.

I checked to see if there was any updates. There was a minor one. I updated, and when I tried to export after the update the background was finally transparent.

HOWEVER!!!!

I had to update a logo, opened Illustrator up again and did my thing and when I exported the PNG the same thing happened. I'm back to seeing a black background. Thinking, have I doubled up Illustrator?? So I close Illustrator and open it from the Creative Cloud app. Nope that's not it.

Help....