Failed preview for large architectural document - Embed API

[testt45725273]

I have a system that usd adobe embed api to display pdf files for a client. Most of the files work fine.
The attached file fails to render for some unknown reason:

I have tried to flatten (convert to embedded image) the file, it increased in size from 2.7 to 12 MB, that way it works in the viewer but its a big problem asking the client to convert all his files.
Any clues?

Thanks