Today i had my project rejected at JLCPCB because they say "there was no bottom solder mask layer file", but there was! My project has no solder pads or any visible copper area on the underside of the board, and it seems EasyEda is not generating a properly formatted BottomSolderMask file in this case, most gerber viewers fail to open or crash while inspecting the gerber file. As soon as i add any visible copper area on the underside, the file is corrected, accepted at JLCPCB, and viewers let me inspect the file.