Try the following:
1) Choose the Plugins->Manage Plugins... menu item.
2) Deselect (to disable) the Harmony Hub plugin checkbox. Wait a few seconds for it to (hopefully shutdown).
3) Re-enable the plugin via the same checkbox. Wait a few seconds for it to start up and connect.
4) Try to edit a plugin action (that is, bring up its action config UI) to see if it works.
5) Repeat steps 2 to 4 two additional times (three times total) to see if it consistently works (or fails).
Then try the following (same thing but via the menu):
1) Choose the Plugins->Harmony Hub->Disable menu item.
2) Re-enable the plugin via the Plugins->Harmony Hub->Enable menu item. Wait a few seconds for it to start up and connect.
3) Try to edit the same plugin action as you did in step #4 above.
4) Repeat steps 1 to 3 two additional times (three times total) to see if it consistently works (or fails).
Copy/paste the Event Log results of all 6 attempts into a post for me and we'll see if we can better determine what is going wrong.