Symptoms

I have couple of lookup columns in the form. The new form does not have an issue. However the edit form throws an error:

"Microsoft.SharePoint.Client.ServerException: The query cannot be completed because the number of lookup columns it contains exceeds the lookup column threshold enforced by the administrator."
 

Diagnoses

There is a limitation in SharePoint that limits the number of lookup columns you can have to 12(List View Lookup Threshold). This limitation is enforced to prevent performance problems when executing too many joins within a single call. AFAIK this threshold cannot be modified in O365, at least not without reaching out Microsoft of which they will more than likely advise that you stayed within the default limit .
Here's one of the many articles that talks about this subject matter: http://blogs.msdn.com/b/spses/archive/2013/12/02/sharepoint-2010-2013-list-view-lookup-threshold-uncovered.aspx

Appit uses CSOM API calls to interact with O365. CSOM enforces the lookup column threshold. With that in mind, the reason why the error is surfaced with the EDIT form and not the NEW form is because the we use the same logic as SharePoint to execute a join to populate data when loading an EDIT form, same can be said for the DISPLAY form. It is this request that is blocked at the API level by the SharePoint List View Lookup Threshold.
 

Resolution

There is no way around this at the moment. Microsoft will not allow for using more than 12 lookup columns in SharePoint Online(O365).
Our Product Management team is investigating alternatives that would allow us to do this in a graceful manner without impacting performance.