This is an old 'bug'/issue. You need to reinstall both products. First Photoshop, then LR. That should fix the issue. Before doing so, you can try setting up the External Editor preferences for the newer version of PS but yeah, when the two are installed as described, there should be nothing further to do. The two products can get disassociated and thus the fix is reinstall both from the CC application (you may need to uninstall but keep references), in the order outlined.