Same situation here. Even removing the directories: .kde, .local and .config (entirely) doesn't help.
I get: kactivitymanage segfault at 7fb3000c3cd0 ip 00007fb2f002e031 sp 00007ffe4f1f29e8 error 4 in libQt5Sql.so.5.4.2[7fb2f001a000+3f000] -- Diego.-
