SUMMARY
Since last update, I can't connect to any wifi network. The networkManager interface doesn't work, no network displays.

I can access to internet via USB modem.

I tried to access to the list of available wifi networks via konsole, but there's only my USB modem that is displayed.

I am pretty sure this has a link with kde as I don't have this problem with lightDE.

My wifi card is the following : 
                      
02:00.0 Network controller [0280]: Intel Corporation Wireless 8260 [8086:24f3] (rev 3a)

The command :

rfkill list

sometimes gives :

1: hci0: Bluetooth
        Soft blocked: no
        Hard blocked: no

and sometimes : 

1: hci0: Bluetooth
        Soft blocked: no
        Hard blocked: no
1384: phy1383: Wireless LAN
        Soft blocked: no
        Hard blocked: no

Just like my network interface is not detected all the time...

I also found out that the command : 

sudo ip link set wlan0 up  

gives me sometimes the following error : 

Cannot find device "wlan0"

and sometimes :

RTNETLINK answers: Input/output error


SOFTWARE/OS VERSIONS
Endeavouros

ADDITIONAL INFORMATION

I have the package linux-firmware