OK, I'm starting to pull my hair out over this one. I've seen it before, but in the past I've been able to at least some guidance from error logs or devmode.
I have a custom page type called "Tour". This page type has around a dozen published pages that are all fine except for just this one. It's blank white. No on-screen error even with ?isDev=1 and turning dev environment on in _config.php. I also set php error_reporting to E_ALL iin _config.php.
Also nothing in my error_logs.
If I change the page type to just a standard "Page", it displays fine. However the custom page type has custom fields so all this data is missing obviously. Change back to "Tour" page type. White page again.
I can only think this has something to do with content. I did find problems a while ago where the user copied and pasted MS Word text into a content field, and that messed up the template, but only from that point of the template onwards. Not the whole thing. I have searched the content and find no MSO code in the HTML.
I have also added an echo to the init() method of the "Tour_Controller". Works for the pages that are functioning, doesn't do anything for this problem page. (So init() is not firing for this one page). I have double checked that the page is the correct type.
Any further ideas on how I can debug this?