I am using Fedora 29, with kernel 5.0.4-200.fc29.x86_64 on KDE. I had a problem with the network connection (wired) where it wasn’t working, and I found that KDE hung on the spash screen after logon if the network connection wasn’t working. Once the network connection was fixed, it logged in ok again.
I’m not on KDE myself so I’ll let someone else see if they can reproduce the issue. In the meantime, could you have a look at the logs to see if there are any errors there?