Dear @greenwing,

greenwing wrote

I am using Omada 5.5.6.
When I update the firmware on this switch to 4.0.1 Build 20220606 Rel.58990, it becomes unmanageable.
 
The switch still functions with its last configuration, but it disconnects from Omada, it is not possible to login via SSH or the serial console.  It accepts the password but hangs before a prompt is displayed.  The only way to recover the switch it to load the backup image and reboot using the serial console.

Thank you for taking the time to post the issue in TP-Link Community!

The issue sounds unusual, our support engineer would like to look into the issue but need to confirm some information with you. Would you mind helping our engineers to check more info?

I've created a support ticket via your registered email address, and the ticket ID is TKID220906181, if you are willing to help, please check your email box and give it a response for follow-up. Thanks!