This is an old issue but it seems that it still happens so I would like to share the solution that I have found.
I have the same issue with my Honor 9 Lite:
Every times I enable USB Debugging, I can see that, when I leave the developer menu and come back, USB debugging is OFF. I can’t keep it ON.
I have found the solution on another web site and it is working for me:
- Disconnect the phone
- Revoke all the USB debugging permissions (on my phone, this option is proposed just after the USB Debugging switch)
- Enable USB Debugging
- Leave the developer menu
- Connect the phone to the PC
- Select ‘transfer files’ option
- Accept the PC certificate fingerprint.