We have configured Hybrid Search between a SharePoint 2013 Farm with an OWA server and O365.
The search results from on-premise appear fine in O365 search but the Preview is not working.
The preview URL is structured as: URLToSite/_Layouts/15/WopiFrame.aspx?sourcedoc..etc.
If you enter this URL directly into the browser it works fine and the Preview image is returned.
On the search results page in O365 we just see a broken link.
Looking at a Fiddler session (not that I know much about interpreting these results) I can see a call to the above URL to get the preview which returns a 302 which seems to be followed by another 302 to the same Url followed by a 401 from the OWA server, the call is to OWAUrl/wv/WordPreviewHandler.ashx?etc.
The SharePoint on-premise site is running in a Claims app using NTLM.
Anyone have any ideas where I can start looking for the cause of the 401?