Sometimes i see jpeg-style artifacts briefly on UI changes even though i have "compressors = none" set in /etc/xpra/conf.d/10_network.conf.
compressors are packet compressors and have nothing to do with image compression. And turning that off is a bad idea, see wiki/PacketEncoding or the manual.
If you want lossless picture updates, set quality to 100% or use a lossless encoding. See wiki/Encodings for further information.
this ticket has been moved to: https://github.com/Xpra-org/xpra/issues/1667