Thank you, it was my stupid mistake. I don't know why but I havent seen newer versions on GitHub when I was updating new board. I think that RC3 is latest. RC6 works well. I'm sorry.

There is probably bug in DWC 2.0.0-RC3, firmware Release 2.03beta3, (web server used from Release 2.03beta3 folder). When I start uploading big G-code (160MB - high detail Groot), web interface imediately crash (Google Chrome reported error with page). Reloading web page helps, but file is not uploaded. (This board is new original Duet 2 WiFi 1.04)
My second board (chinnese probably 1.02 with few weeks older firmware) works without any problems. I'm sorry but actully I'm not able to test combination of board/firmware/SD card.