When exporting TIFF files as different art boards only one layer displays.

I found the cause was that one of the layers was selected. This is the only item that was showing in the exported files.

By simply deselecting the layer the whole file exports properly as expected.

The two exported files are from the same document…

The one with just the blue background is the one with the background selected making it the only thing showing.

The other file was from the same document with nothing selected displaying both flags and background.