Dear,
I am new with the Omnibus F4 control board and I have already a problem. When I was exploring the board with a Betaflight configurator I dissconnect the USB button(save and reboot) and now write “Failed to open serial port”. I am trying with the drivers installed (recommended) and ImpulseRC(still searching), with Zadig I do not see anything like STM32? I ma using windows10(64). Do you now any solution?thanks
Your usb port may have locked up.
Try rebooting your computer it can help sometimes.
I tried many times and did not help. Thanks
I think there is no need to explain 
Luca 
swapping usb cables and usb ports on your computer?
You could trying putting the board into DFU mode.
By holding a boot switch while you plug it into your computer.
Run the ImplulseRC tool
Then try reflashing the board.
I was searching all day today and now when i saw all movies on youtube, try impulseRC fixer and Zadig, different USB cables and now I tried the third port of USB on my computer, push the boot button and suddenly work and ImpulseRC fix the problem. I was flashing the board and now it is normal. And I am still do not know, what is the problem…USB ports, cables?Thanks
Its a Windowism.
Sometimes windows plays how you want, sometimes it just stops for no reason.
Glad your back up and running
This is a helpful link Making Flight Controller Connect Through USB - YouTube