Site and List (Library) Permissions with Lookup column

Question

After sharing a Sub-Site with an external user (requiring Microsoft live login) the external user cannot access a document library within the site.
I'm getting the "Sorry, you don't have access to this page" response.

Initially, when I tested sharing on a different site collection, the external user could access the library fine.
Differences between test library and current library:

• Current library has Approve/Reject and Versioning
• Current library has a Column (defined at the top site) that is a lookup to a list (also on the top site).
• Library page has a Query URL String web part which provides a filter targetting the lookup column.
• Library has 2010 and 2013 workflows.
• Librarys new and modify form have been modified through web-editor, runs Javascript.

Top Site** - ListA - Int Sites - Ext Site Hub - Ext SiteB - LibraryC

List A is at s.sharepoint.com/sites/Top/Lists/ListA
External Site B is at s.sharepoint.com/sites/Top/Ext/ExtB
Library C is at s.sharepoint.com/sites/Top/Ext/ExtB/LibC
**Columns and Content Types for LibraryC are defined here

In O365 Admin I have selected Allow external users who accept sharing invitations and sign in as authenticated users.
The in SiteB I clicked the Share button on the site ribbon (next to the Follow button), and invited the external user, assigning them to Team Member (Edit).
Once the email arrived, I followed the link making sure to log in the with the correct Live account.
This took me to SiteB, and when I tried to navigate to the library, I got Page permission error.

I have tried removing and re-adding the users permissions. I have tried making the site/library permissions unique/inherit.

What have I missed?
Is this actually possible?
Has Sharepoint hidden some weird set of permissions for this?

Any help is appreciated.

Answer 1

Turns out:

Quick Links are different between different people/groups. The Library wasn't showing in the Quick Links so I assumed that I couldn't access it.

Document Version Draft Item Security was set to Approve + Author only. When following a direct link, it would take me to an empty library.

Solution: Setting Draft Item Security to 'Any user who can read items' and adding the library to the other users quick links.