Short of contacting Canvas support, the only thing that I can think of that might work from the web UI is to try tacking /undelete onto the end of your course homepage. It shows you a list of recently deleted items and it may allow you to restore the page that was deleted.
The null is going to be problematic, though. That basically means that something is missing, undefined, or not present. Whatever information that is might be necessary to restore it.
If the problem is very recent (it was working prior to July 18 but it's not now), then you might be able to go to your test instance of Canvas and look through the list of pages there and compare it to the list of pages inside your course to see what page got deleted. You could then try exporting the content from the test instance and importing it into your course, overriding items with the same ID.
There are other things that might be doable through the Canvas API, but those are advanced topics. Support may be able to track it down a lot faster.
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