Page will not update depending on content

I can hardly believe I’m posting this, but I’m not sure how to debug it. I have a site where I can’t update a page depending on what words are in the page content. It’s hard to know what the trigger is without any clear error message.

If I change the sentence “… invasive species strategy to include implications of climate change and determine clear priorities and performance measures to guide future work”

to: “invasive species strategy to include implications of climate change and set clear priorities and performance measures to guide future work”

(yes, the word “determine” was changed to “set”)

The page will not update! When you press the Update button it returns to the url /wp-admin/post.php with essentially an empty page (content-wise).

(This is a very simple page — a few paragraphs of text and one link.)

Similar seemingly innocuous changes trigger the same behavior on this page and now we’ve seen it in another page. Suffice it to say I’m more than a bit worried.

I’m going to attempt to enable WP_DEBUG type stuff in the hopes that there might be an error message buried somewhere — but I thought I’d ask here to see if anyone had experienced anything like this. (Searches of this forum didn’t turn up anything similar, but frankly I can’t think of good search terms for this problem.)

Thanks for any suggestions.