Double-check WS is listed as 'allowed' in the OSX firewall. If it's not listed then you will need to add it. Description here.

Try deleting your WS preferences folder whilst WS is closed. But first retain the file called downloads.dat. (This can be re-added back to the WS prefs later whilst WS is closed.) Then start up WS again. You will probably need to re-add the forwarded port in the Listening Ports section of settings. Does it improve things?

Another thing to try would be if you have another account on your computer. Or if you set up a test account & open the program from there. It's easy to setup a new account and delete later. The only added complication a 2nd account would have would be the port forwarding because pf is usually per program per account & no two programs or accounts can pf the same port. But UPnP might work without it anyway at least for a period.

After your WS connects let it run for a noticeable period of time.

* Note: the next WS release will have GWC support re-added to help with connections (GWC support was dropped after LW 4.12 and replaced with UHC support instead.)