Ubuntu Core Desktop will not be released alongside Ubuntu 24.04 LTS in April, as originally hoped.
Canonical doesn’t go into details about what specific issues need resolving. One imagines, given that the first Ubuntu Core Desktop release was going to be a preview and not a recommended download, it’s a myriad bugs/difficulties — ones not easily sorted.
They probably realized snaps are garbage and are still trying to desperately un-garbage them before the release.