When checking "Watch all content in this space" you are "subscribed" to notifications for all CURRENT pages in that space.
When a NEW Page is created you are not notified, and are not even "subscribed" to that (new) page or further content updates / changes.
This is not normal behavior.
I should be notified whenever NEW pages are created AND also when those update, otherwise why would I watch an entire space?
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Upon further research this only happened on one page. No watching user was notified and confluence is not "seeing" the page as updated...
Might be a glitch?