These steps from support fixed it right away. Also, to my surprise, after Cosmos loaded back up it remembered any models I had previously downloaded. Nice.
Mac OS Steps:
Please uninstall Chaos Cosmos from Applications, then delete the cpkg.db and cpkg.meta files from your documents in the Chaos Cosmos folder. If they are not there, please open ~/Library/ApplicationSupport/Chaos/Cosmos/DB and delete them from there. However, those 2 files must be deleted before reinstalling Cosmos.