Pixhawk: Failure to download new firmware

Hello! I am new to quadcopters. Bought a Pixhawk PX4. Want to install Mission Planner firmware, from Ubuntu 18 (running “Mono”). I get a message “Failed to download new firmware: System.Net.Web Exception: the operation has time out…” etc.
Previously, I tried to install other firmware, from QGroundControl and APM Planner. Can you help with this problem?
I also get messages such as “Bad Param, GF_count=nan”, “Bad Param, com_fltmode3=nan”, etc.
Please, send a copy of your reply to my e-mail: TommyJoad2017@gmail.com
Thanks, Gennady