Hm, I am not sure, but it could be that the old KDE configurations files do not match with the newer KDE version you now have. Normally, when one upgrades from an up-to-date Leap version to the next, that is not a problem. New KDE will then see the old file(s) and convert them (if that is to be done). But the step from Leap to Tumbleweed might be to great.
You could try to create a new user (from the console login at e.g. Ctrl-Alt-F1) with yast and then see if that user works.
You could also rename the configuration files of the user (.config, .local, I am not sure that is all) and then log-out - log-in.