.0 versions can contain bugs not found in the pre-launch versions. You can help us get them removed by reporting them. And look out for updates to Plasma, as they will come with many fixes over the next few weeks!
As for the themes and widgets created by third parties, we have already publicly advised developers to port their stuff. We have two pages available to guide them, one for themes, one for widgets.
If you, the user, discover your favourite theme or widget is failing, please look for it in the KDE Store and notify the author, as KDE has no control or leverage over third party developers.
Thank you
Some distros (Fedora at least) have debuginfod integration,meaning that gdb will automatically download debuginfo files. The downside is that it will take a while for download to finish (for the first time at least) since it gets symbols for all linked and loaded libraries recursively, and it will take a few gigabytes in ~/.cache.