Animate - Bitmap not appearing after publish

I'm working on an HTML5 game I've been creating with Animate. I wanted to create a brick style background. So I drew a bunch of rectangles to look like a brick. Converted that drawing into a symbol and then converted that to bitmap. Then I used that as the background color for a rectangle that I drew covering the whole stage. The design looks about as I'd expect in the editor.

I mean... the original version was a bit bright, perhaps I should've used a more toned down orange... anyway I then drew another black square on a layer above and dropped the alpha channel so it darken the background a little. And this is the effect.

Buuuuuut.... when I test (aka publish, aka view in the browser) the project it looks like this

The gradient background that appears is from another layer bellow. Basically the darkening layer is still there, but the bitmap drawing is gone. why?

Can anyone help me with this?

PS: just to add insult to injury, in another frame I'm also using a bitmap, that's an icon.png and it does render in the browser. (it's the hand icon)