I really love the look of KDE plasma 5 and also the memory optimization done for the desktop, after disabling all effects the desktop becomes more usable and responsive, it's beautiful design and the platform has many features. I used to work on MATE for more than 5 years but now I tried to give KDE a try and after installing Kubuntu 19.10 I found many problems :
[*] Every time I start adding or removing desktop widgets the whole plasma desktop crashes and I should relaunch it again from terminal or force shutdown my machine.
[*] Sometimes when I close an app like artha from notification area the app is reported as crashed and kde-apport start to consume cpu.
[*] There is no way to disable apport even after setting 0 inside config file, the apport service is always started ! is apport used mainly by any kde apps ?
[*] Every app : ksysguard, Marble, Kig, Elisa, KOrganizer, Falkon, KDE settings, at some point crashes without any reason, I don't know why but this is bad, because other non kde apps like firefox, vscode, libreoffice writer... are stable and work fine.
[*] Sometimes Vaults does not accept my password, and I should reboot many times to get it working and accepting my password to access my hidden files.
[*] plasma-nm is generating infinitely the same message "plasma-nm: Wireless scan on "wlp7s0" failed: "Scanning not allowed at this time" inside .xsession-errors file
[*] I use dark theme but when running any app in root mode it's white, this really hurts my eyes a lot and gives some inconsistency for plasma desktop, apps launched with root should inherit current user theme.
[*] The mpd service is slowing down my boot for more than 1min40sec, it generates the following error in log "mpd.socket: Failed to create listening socket ([::]:6600): Address already in use", I removed mpd with cantata, I hope that there is no other plasma component that needs mpd to run.
[*] Some non kde (virtualbox, artha, gimp, inkscape...) apps looks bad with dark theme, and many times text could not be read on them.

I think plasma desktop should stop adding more tweaks and focus on fixing and optimizing current desktop, because it's great desktop but it gives me insecurity to use it for something serious, I'm always afraid the desktop will crash and I will lose my data !
With MATE I could run my machine for a week without any crashes, even the desktop was ugly but everything was stable and desktop never crashed.