Hi,
My Arduino mkr1010 Wifi gets sometimes stuck sometimes while loading the firmware. But i just disconnect usb, and connect it, I press again the "upload" button and it works. In my case I am not using windodws but ubuntu.
To write the new sw in the microcontroller, it must enter in bootloader mode, from there, the flash is erased and writen, and at this point your computer detects bootloader. Once reset is done the device enters normal mode and the computer should detect the right com port..
Once I had a similiar problem with another microcontroller and Windows, and windows was to blame at that time...
I would try to disconnect your arduino, restart your computer, connect your arduino and open the ide again...