Random unreproducable issues in Membership Logins

Greetings,

We are having quite a few clients contact us with problems accessing restricted content on our site. We have memberships set up with negative access rules and some clients are finding that when they attempt to access random yet specific content they are redirected to the protected content page. I say random yet specific because the relationship appears to be between client and page/post not membership and category.

Sometimes resubmitting a post will solve the issue, other times clearing cookies/trying a new browser helps.

One client reported that they could view the post and summary in a category page but when they hit the link to access the post itself it redirected them to the protected content page. They could access other posts in the category. This was solved by resubmitting the post.

I have been unable to reproduce any of the issues on my PC with my account but the site owner has sent through a number of examples of people having issues.

Can you shed any light on what steps we can take to resolve these random issues?

We are using the wordpress login page for members to log in and have the admin bar hidden from the front end of the site.

The site does have caching, but this is turned off for logged in users.

Are there any session or cookie requirements we need to set up?

Regards,
Laura