When an event has a scheduled registration period, the "Register" button should be shown on the event instance page as soon as the registration window opens. Similarly, when registration closes, the button should disappear automatically. Currently this doesn't happen, the button only appears / disappears after the cache is cleared.
Expected behavior: The button should appear.
Actual behavior: The button doesn't appear, only does so after clearing the cache.
Provide a cache context on the button that varies by the registration open / closed status.
Due to limitations in the cache implementation in Drupal core (ref. 🐛 [pp-3] Bubbling of elements' max-age to the page's headers and the page cache Postponed ), this will not work for anonymous users unless a workaround is applied:
Active
2.0
Recurring Events Registration (Submodule)
Another solution for anonymous users could be to load the register button via ajax. I've successfully used this for elements on a page that need to be outside of cache context for anonymous users.