I have the same problem under Windows 10 = cannot upload to the UNO R4 WiFi (or the Minima).
The upload process causes a momentary disconnection and then Windows sees it as being on a different COM port when it reconnects.
The upload starts during the disconnection and then times out because the board virtually moved ports.
Even hitting the reset button causes a momentary disconnection with my laptop.
FWIW I am having a similar issue with GIGA R1