I didn’t understand when and why, but plasma freeze:
Using dolphin to copy many files from more than one folder on the network using smb:// and sftp:// .
Using rsync with luckybackup .
I noted that it happen when the copy process last much time, about 20minutes or more, if the copy process last few minutes it doesn’t freeze.
The freeze means that if I leftclick on the taskbar or on any icon on the panel or rightclick on the desktop nothing happens, but if I click on an application window like dolphin or chrome the click is ok.
Did somebody noted this behaviour??
And to have again plasma I have to ctrl>backspace(twice) and relogin to have plasma again, this is quite annoying, but, how can I restart plasma without ctrl>backspace(twice)??
manythanks, ciao 
pier
my system is running plasma 5.6.3:
PC=Dell latitude E6510, RAM=8Gb, GPU=GT218 NVS 3100M, CPU=i7 Q 720 @ 1.60GHz
upgraded 13.2 to leap 42.1, using wolfi repos. I’m running KDE 4.14.18 and plasma 5.6.4, KDE frameworks 5.22.0, KDE applications 16.04.1, Kernel 4.1.21-14-default