I seem to have the same issue, although I have no idea what it causing it just yet.
However, running pkcon get-distro-upgrades also never returns, but does show errors. (Found that here)
$ pkcon get-distro-upgrades
Getting upgrades [=========================]
Finished [ ] (0%)
(pkcon:30972): GLib-GIO-CRITICAL **: 15:34:48.751: g_task_return_error: assertion 'error != NULL' failed
(pkcon:30972): GLib-GIO-CRITICAL **: 15:34:48.751: GTask 0x5588c58c4a80 (source object: 0x5588c58c6240, source tag: 0x73f8baa01ed0) finalized without ever returning (using g_task_return_*()). This potentially indicates a bug in the program.
[=========================]
Waiting in queue [ == ]
I suspect this might be the root cause, but so far I can’t get pkcon to spit anything useful about what is happening.