I had 3 Deco M4R working fine.

I added a new Deco XE75 to the network/mesh, then set it as main deco.

Since that (2 days ago) the wifi setup is empty: no ssid, no password shown. 

I tried to enter both fields manually but "save" is disabled.

Tried rebooting the network, it didn't worked.

I was afraid the network was running without password, but using a cell, remove the connection, connected again to the wifi and I can confirm (thank god) the network is password protected.

How can I fix that?