A bug in the Solid framework (https://bugs.kde.org/show_bug.cgi?id=391706 ) broke auto-mounting internal disks (among other things) in Frameworks 5.44 and 5.45. The bug was fixed in 5.46.
However, Kubuntu shipped with 5.44, exposing users to the bug. See for example this bug report from a Kubuntu user that we got yesterday: https://bugs.kde.org/show_bug.cgi?id=397911.
We should consider backporting the fix (https://cgit.kde.org/solid.git/commit/?id=122a6cd8989a4bd3096fddea908a1c2b223be62a) to Frameworks 5.44.