ConnectForSharepoint does not update the correct list of files

Description

Steps to reproduce:

1. Create two document Libraries on the SharePoint site, Doc_Store and Vid_Store.
2. Upload documents to Doc_Store folder.
3. Run the SharePoint Update job for the first time.
4. Upload documents to Vid_Store folder.
5. Run the SharePoint Update job for the second time.
==> In EPiServer CMS: Doc_Store folder's documents disappear. Vid_Store folder shows its documents.
6. Run the SharePoint Update job for the third time.
==> In EPiServer CMS: Doc_Store folder shows its documents. Vid_Store folder's documents disappear.

Expected: The add-on shows the list of documents for each selected SharePoint folder.

Actual: The add-on shows and hides a folder's documents each time the SharePoint job is run.

Environment information:

• EPiServer CMS 10.10.4
• EPiServer.ConnectForSharePoint 2.2.1
• SharePoint Enterprise 2013 15.0.4571.1502 on premises