One of the websites we manage, http://wesleyunited.ca , recently started having a problem with menu aliases containing "contact" as a substring: clicking the menu just brings up an empty page that just says "Temporarily Unavailable." This happened spontaneously, we didn't do any work on the website or update anything manually before this problem arose. After we found out about the issue we updated to Joomla 3.9.5 (this was a few weeks ago) but that didn't fix the problem.
As a temporary fix I changed the "Contact Us" menu item's alias so that is doesn't contain "contact", and I made a "Contact (Broken)" sub-menu item which exhibits the error for demonstration purposes.
I played around with different aliases, and found that as long as "contact" is a substring it will not work, but everything I tried without it was fine. Even "contac" and "ontact" work. It also doesn't have to be separated out with hyphens, something like "blcontactah" will cause the error. I tried adding "contact" to the aliases of the other menu items (not just the "Contact Us" page) and it broke those as well. Even if a menu item has "contact" in the alias and a sub-menu item does not, the sub-menu's link will still give the error, I guess because "contact" is still in the url.
Does anyone have any idea for why this is happening? Did our server spontaneously decide to start blocking urls containing the string "contact", and if so how do I disable that?