When you use the "This page" expression as a datasource in a scheduled custom event workflow action, it won't evaluate to the originating page. Instead, it returns null. This happens because scheduled custom events don't retain page context at the time they run — so the expression can't resolve to a specific page.
What you might notice
A custom event that works when triggered directly fails silently when scheduled
Actions inside the scheduled custom event that depend on page data don't behave as expected
Referencing "This page" in the scheduled event's datasource results in a null value at runtime
Workaround
Instead of using "This page" as the datasource, reference the specific page element directly — for example, use "index" instead. This ensures the value resolves correctly when the event runs.
Status
We're aware of this limitation. Because there's a straightforward workaround, it's not currently a high priority to fix — but it's on our radar for the longer term.