What is the problem?
Can't reconnect after a power cycle. Normal power cycle or emergent power off seem to make no difference. I have a random bug with Marlins UBL where after some prints the Z offsets drifts a crazy amount. Really annoying... In such emergent case I power off the device through the power supply to not damage the bed any further. The USB is still connected then. This is on WIN10 as I test Octoprint till I have PI in the mail box. Powering on again and Octoprint can't reconnect. BTW why it doesn't try to reconnect automatically?
What did you already try to solve it?
Checked the USB cable. Taped the 5V connection from PC which is great for another reason but didn't resolve the issue. Changed a seriell port related registry entry as fix mentioned here on the forum.
There is the advice to install the Maple driver but its not possible as the driver is not signed and whatever I tried my machine doesn't want to install it. The connection is there so I don't know if the Maple driver is really essential.
Have you tried running in safe mode?
Did running in safe mode solve the problem?
Changing monitoring state from "Offline" to "Opening serial connection"
Connecting to port COM3, baudrate 115200
Changing monitoring state from "Opening serial connection" to "Error: Connection error, see Terminal tab"
Changing monitoring state from "Error: Connection error, see Terminal tab" to "Offline (Error: Connection error, see Terminal tab)"
Unexpected error while connecting to serial port COM3, baudrate 115200 from hook default: SerialException: 'could not open port 'COM3': PermissionError(13, 'Zugriff verweigert', None, 5)' @ comm.py:_open_serial:3666
What is interesting there seems to be an PermissionError after this happens but I couldn't find any solution for it. Is there anything I could try?
Additional information about your setup
Latest Octoprint on WIN10 with a SKR mini E3 2.0 on an Ender 3