We are having issues with the new Excel Web AddIn (Javascript API). The formulas are getting corrupt on initial load of the file from One Drive. If we go in to Addins and Refresh the Addin, it works.
Proper formula name: GET_CUSTOM_DATA()
Corrupted name:
=xxxx_xldudf_GET_CUSTOM_DATA()
Formulas auto correct to the proper name when the addin is reloaded. This can be either through readding the addin through the 'Insert' Tab and 'My Addins'. Or by clearing the excel cache and letting the addin reload itself on Excel restart.