HiI have not got the private message we need your email to get in touch with you on this.please do send me the emailthanks 

Please contact the local Adobe account manager 

Are all the bundles active?

Is it happening on every letter/document?

Can you please give us the version of the solution?

You can safely continue to use adobe live cycle designer. The old Adobe Livecycle designer has been rebranded and is now called AEM Forms DesignerThe new forms designer is fully supported by Adobe

Yes , we do that all the time convert json to appropriate xml to merge with template 

Can you send the xdp and data file?

No it is not possible you have to pass xml to merge data