optipng optimization level @ 2 (default)
pngout optimization level @ 2 (default)
Some PNG are "large" ~800kb (and you are right, should had been JPGs, but ..)
But some are small ~5kb big Logos with opacity, and they fail, too.
But not the Picture fails, but the Database!?!
The file(s) where well converted and are laying around fine on the server.
But the correct Info about the new Filename was not stored to the DB.
So there must be a "check" function failing or such.
And I would be helpful, if another check run thought, before the org. gets killed.
Checking if all Data is fine .. Files .. Wordpress Resize files AND the DB. :)
BTW: The PNG to JPG sets also the wrong BG, not the set #ffffff but #000000.
(Don't know if this helps ..)
So I convert the PNGs local now and re-upload them, if I have to do it anyway.
Or is there a way to fix the database .. somehow.