Available updates not appearing in App Store > Updates

There's an update to TickTick. When I look at TickTick in the App Store, there's an Update button. The update is compatible with my OS, according to the "compatibility" part of the TickTick page on the App Store. But the Updates tab of the App Store shows no updates available, even after a manual refresh.

When I click the "Update" button the TickTick page, the button show it's been clicked, and the progress-spinner GIF appears in the toolbar...and that's all. The app never updates. The spinner never stops spinning.

Kinda makes me wonder what other updates are out there I'm not being informed of.

Suggestions?