First visit to MODx page after session expired always redirects to homepage

If I enter a valid URL to an article on my site I am always redirected to the homepage. Once I have visited the homepage, presumably refreshing my session, I am able to go back to the document I requested.

This also happens when I am on a page, leave it overnight, then press refresh. Even though the URL in the browser is valid, I am redirected to the homepage. If I then re-enter the identical URL, I am taken to the page I want.

I'm on Evo 0.9.6

Any ideas?

My client has ignored this, but it is now a problem as I am trying to auto-generate a sitemap.xml and Google is being redirected to the homepage. Until now sitemap.xml has been a manually updated file, and this works fine with no redirection, (hence me suspecting the session problem is related to MODx). I have looked through the settings but can find nothing about restricting access to the public site. I have Googled but I can't think of good keywords, so I may have missed a post somewhere.

Huge thanks.

There is a user group and document group, used to give access to one page that is privileged. Would this mean MODx checks all visitors even to pages that aren't in this group?

We have JoCo and QuickEdit extensions installed.

I've found something worse. If I turn off cookies in my browser, the site goes into an infinite redirect.

How can I turn cookie authentication off for public visitors to the site? If not that, then for Google or sitemap.xml?

(I have ticked "searchable" on the page settings.)

Title: sitemap.xml
Long title: (Not set)
Description: (Not set)
Summary (introtext): (Not set)
Type: Document
Document's alias: sitemap.xml
Keywords: (Not set)
META tags: (Not set)

Changes
Created: 12-07-2013 10:42:46 (chris)
Edited: 12-07-2013 11:19:24 (chris)

Status
Status: Published
Publish date: (Not set)
Un-publish date: (Not set)
Cacheable: Yes
Searchable: Yes
Menu index: 36
Show in menu: No
Web access: Public
Manager access: Public

Markup/structure
Uses template:
Edit using rich text editor: No
Document is container: No

My PHP session settings..

session
Session Support enabled
Registered save handlers files user sqlite
Registered serializer handlers php php_binary wddx

Directive Local Value Master Value
session.auto_start Off Off
session.bug_compat_42 Off Off
session.bug_compat_warn On On
session.cache_expire 180 180
session.cache_limiter nocache nocache
session.cookie_domain no value no value
session.cookie_httponly Off Off
session.cookie_lifetime 0 0
session.cookie_path / /
session.cookie_secure Off Off
session.entropy_file no value no value
session.entropy_length 0 0
session.gc_divisor 1000 1000
session.gc_maxlifetime 1440 1440
session.gc_probability 1 1
session.hash_bits_per_character 5 5
session.hash_function 0 0
session.name PHPSESSID PHPSESSID
session.referer_check no value no value
session.save_handler files files
session.save_path /tmp /tmp
session.serialize_handler php php
session.use_cookies On On
session.use_only_cookies Off Off
session.use_trans_sid 0 0

In case it is relevant, the home page is not the default redirect for a wrong URL. If once I have a cookie set up I enter a URL that doesn't exist, I'm redirected to a "page not found" page, rather than the home page.

I've tried including the following in the snippet but it doesn't change anything. (Was an admittedly desperate attempt!)

I found a (horrible) solution, posted here:
http://forums.modx.com/thread/8229/modx-site-that-doesn-t-use-cookies?page=2#dis-post-471636