So a customer requested an update to their PHP configuration file (we give them their own .ini file but they cannot access it directly because WE ARE JOB CREATORS). Evidently a WordPress plugin needed the max_input_vars increased (it's 1000 already ARE YOU TRYING TO NAIL DOWN EVERY SHINGLE ALL AT ONCE? Strong roof, that). Easy change, just modify the line and back to the BBQ.
I checked --the right php.ini file is loaded. The new change took, but now previously edited items are showing undefined values. Whuh?
Well, it seems phpinfo will not necessarily inform you if you have a syntax error in the php.ini file. You know, something dumb like using a colon instead of a semi-colon for a comment. DUHRRR.
Important safety tip: Check your colons, people.