I have a DFRobot Romeo V2 board, that i bought for a little line following robot project.
I have been successfully communicating with the board via Arduino IDE with the COM device set as a Leonardo. And have been successfully uploading code to it.
Had tested my robot then plugged in to upload edited code, like an idiot I prematurely removed USB before it had finished uploading.
Now I cannot maintain connection with the PC, it appears in my Device Manager then drops connection again.
If you hit the reset button the board goes into bootloader mode for a few seconds. Try to hit the button late enough to still be in that mode when the upload starts but early enough that your PC got the serial device activated when the upload should happen.
Don't upload your sketch but one of the basic sketches (p.e. Blink). That because these problems are caused by a non-working sketch that freezes the CPU (often an endless loop or wrong usage of interrupts).
This morning I managed to recover it just how you suggested.
I was getting frustrated with it so decided to just send a simple small code to it, and catch it whilst it was connected for a small amount of time. And it worked.