Yes, specifically in relation to what are known as “transferable sites” on WPEngine. “Transferable sites” are developer sites that sit behind two layers of password protection until transferred to the client.
GravityMerge works as expected on normal installations of WordPress on WPEngine. It also works on “transferable sites” but one feature does not work on transferable sites. If you have your Form > Settings > GravityMerge set to ‘Delete Document’ (instead of ‘Save Document’), the merged document will not be available for download and will produce a browser error stating something like “File wasn’t available on site”. You can still email the document, but downloads will not work when Form > Settings > GravityMerge is set to ‘Delete Document’ (downloads do work if Form > Settings > GravityMerge are set to ‘Save Document’).
This issue appears to be unique to transferable sites, and does not occur with normal installations on WPEngine.