This post highlights some potential pitfalls when setting up xDB on a Sitecore 8.x environment.

1. Alternate DefaultLanguage

When you have set a DefaultLanguage other than “en”, you might run in to the following issue:

• No Contacts appear in the Experience Profile app

To fix the this issue, you need to set the Analytics default language (matching your DefaultLanguage) in order for the contacts to be queried correctly from the analytics index:

<setting name="ContentSearch.Analytics.DefaultLanguage">
   <patch:attribute name="value">de-DE</patch:attribute>
</setting>

Thanks to Sitecore Support for pointing this out.

2. No Timeline is showing in Experience Profile

This might happen after upgrading from a previous version due to missing channel images. There is an error in the Ajax response related to missing media items. (Could not get media stream for image with id)

Solution: Go to a fresh install of Sitecore 8.x (corresponding to your version). Create a Sitecore package containing all sub-items from the following path:

/sitecore/media library/System/Channel Images

Install this package on the instance that is not working and it should now show the timeline again.