The validation bug is in 5.8.9 and it manifests when a field fails validation. No feedback about the errant field is provided to the user and one is not prevented from submitting the page. So it looks like “Page updated” but it hasn’t.
That’s really not here or there for this issue however. The 5.8.9 bug was simply the motivation for me to update to 5.9.5, which upon attempting to save any changes, produces the Uncaught Error above.
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