If network mount (CIFS) is stuck due to server unavailability, then Plasma freezes making its impossible to switch windows via taskbar. If it is manually killed and restarted, it does not draw itself and following output is shown: plasma(4224): Communication problem with "plasma" , it probably crashed. Error message was: "org.freedesktop.DBus.Error.NoReply" : " "Did not receive a reply. Possible causes include: the remote application did not send a reply, the message bus security policy blocked the reply, the reply timeout expired, or the network connection was broken." " The only way to restore functionality is to recover or unmount remote share and then restart plasma.
(cifs) mounted where? is it part of your homedir or other?
CIFS mounted on /mnt/some-share. Homedir - no.
This issue needs to be reported upstream to http://bugs.kde.org. Please remember to add upstream report info to this report once you are done.
https://bugs.kde.org/show_bug.cgi?id=184062
Thanks for reporting upstream. Will monitor for a resolution.