I had the same issue as the OP and I have installed Enpass on various computers and mobile devices and every time I have restored from Google it has been my Google password that has worked and now like the OP, this is not the case. The only passwords I have used with Enpass have been my Google password to restore my data and the Enpass Master PW. Neither work on a new installation I was attempting and I have no clue what the 'password of data' refers to as it should be the Google password which is global to everything google, i.e., google, gmail, gdrive, etc.
@devil - I manage to get around the above issue by creating a local backup and restoring my vault on the new install from that. Afterwards I went to the vault and set up the sync using my Google password and it worked so if you read this, that is a work-around.