WebUI : I cannot access to Volumio WebUI

I use 2 Raspberry with Volumio.
First with volumio 3 ; second again 2.
My issue is, since yesterday, I did not have access to volumio (2) on web interface.
I can ping it ; I can connect a keyboard and a screen, but I cannot access it by webUI (neither by the interface of the first Rasberry, neither by its own IP address.
Which service should I restart ?
Thank you