The same thing seems to have happened to mine. I had 3 activities which were working as expected and now none of them do anything. The activity button (A, B, C) lights up as usual, but buttons assigned to those activities act as though they are not configured at all. I don't think I can even start over because the app doesn't let me create, open, or save activities (all grayed out). And even if I did go through the tedium of re-creating everything from scratch, do we have any reason to think we wouldn't just get hit with another sync error?
Nothing at all changed with the app/remote setup since the last time I was able to sync normally (a month or so?) aside from probably macOS updates. Can't rule out that might be involved but it would seem pretty strange.
Looking around the forum I haven't seen dev/support replies in a few weeks...I hope everything's OK with these guys and the project.
Edit: I now see recent replies from Jason etc....sorry for the misinfo. Hope they can chime in here on this.