The app said "my license code is no longer valid" even though I never changed anything, and re-entering the key only worked after many attempts. (fixed in v1.6.6)

That was a real bug on our side, fixed in v1.6.6. Older versions could misread a momentary license-server problem as "license revoked" and delete the locally stored key — which is why the app then demanded the key at every launch, and why hammering Activate eventually worked (one attempt would land on a healthy response). Since

v1.6.6 a server hiccup can never sign you out: your stored license stays put and the 30-day offline grace covers the gap. If this happened to you before updating, activate

once more after the update and it will not recur.