I'm having some trouble flashing CircuitPython to my Circuit Python Express. I successfully enter boot mode (LEDs are all green and red D13 light slowly blinking) but I can't flash anything. When I drag and drop a .uf2 file, there's no response even though I see the .uf2 successfully copied to the CPE drive. Eventually, CPE exits boot mode and returns to flashing rainbow lights. When I double click reset to enter boot mode again, the file I had dragged and dropped is gone.
Has anyone encountered something like this before?