I updated to 0.15.10 shortly after I posted this and the problem resolved itself.

Thanks!

I just updated to Factorio 0.15.9 and now I have these big groups of white bars that float across the screen.

Almost looks like it's supposed to be clouds or something and the image files are missing.

Doesn't seem to interfere with game play, other than just being distracting.

Log file...

0.000 ...