Issue
In the DITA source there is an xref which looks like the following
<xref href="../yourdirectory/yourfile.html" format="html" scope="external">Link Text</xref>
and one that is for
<xref href="yourdirectory/yourfile.html format="html" scope="external">Link Text</xref>
When viewing the output in Reverb, the second xref works but the first one doesn't.
Solution
The problem is caused by a Reverb specific behavior. Reverb allows help parcels to be added/removed dynamically. As a result, Reverb disables links which it believes belong to a missing help parcel and will therefore be invalid. This behavior can be inhibited by telling Reverb 'yourdirectory' links are valid and should not be disabled. This is accomplished by creating an override for 'Pages\scripts\connect.js' and replacing the code for the following lines:
Connect.parcel_prefixes = {};
Connect.parcel_prefixes[Connect.base_url + 'connect/'] = true;to
Connect.parcel_prefixes = {};
Connect.parcel_prefixes[Connect.base_url + 'connect/'] = true;
Connect.parcel_prefixes[Connect.base_url + 'yourdirectory/'] = true;