After stop/start of NetworkManager plasma-nm5 will not show all available
connections.

To reproduce:

1.) Install Tumbleweed or start Tumbleweed KDE Live media
2.) login as user
3.) Use the connection editor of the plasma-nm5-applet to create a connection
to an existing WIFI SSID. Set the connection to "autoconnect=false". Use a
static IP and define DNS-server-addresses. Store network secret in kdewallet.
4.) Reboot system and log in as the same user as before
5.) Test the created WIFI-connection (establish connection, test and then
terminate it)
6.) Open a console and do
> su
Password
# systemctl stop NetworkManager.service
# systemctl start NetworkManager.service
# exit
>
7.) Check list of connections offered by plasma-nm5-applet

Result:
The WIFI-connection is not shown anymore. Only the available SSIDs are listed.

Expected result:
The WIFI-connection is listed and can be selected.

# nmcli c
shows the connection (and nmcli will allow to use it).

# journalctl -b 0 -p4 NetworkManager
shows no errors

# systemctl status NetworkManager.service
shows NetworkManager is running without any problems

If the connection is set to "autoconnect=true" it will be  established
automatically after stop/start of NetworkManager and will be listed in
plasma-nm5-applet.

My System:

openSUSE Tumbleweed 20190226
KDE Plasma Version: 5.15.0
KDE Frameworks Version: 5.55.0
Qt Version: 5.12.0
Kernel Version: 4.20.10-1-default
OS Type: 64-bit
Intel Wireless 8265/8275 driver: iwlwifi
IPv6 disabled
firewalld enabled
static IP4-address, 2 DNS addresses and firewall zone are defined in connection
file in "/etc/NetworkManager/system-connections"
my router controls wifi access via  MAC address filter

On the same system with openSUSE Leap 15.0 the above procedure delivers the
expected result.

I discussed the problem here:
https://forums.opensuse.org/showthread.php/535097-No-more-WIFI-access-after-start-stop-of-NetworkManager
without result.