Ok solved by flashing "backup_20180511" firmware posted by serg2327 in this thread.

Hi there, i've flashed the backup you named "Blackview_A20_backupFT_2",  now when i boot up the smartphone asks for a password? what is that? Maybe i need to unlock the gapps, but using the frp.img bundled in the archive i've got error "Obtain DRAM failed" "Please check you ...

I've tried by disabling all admin apps in settings menu, then i went to disable google play services, cleared cache and all date, then i've reenabled again, but got no result.

Maybe do i need to reflash the rom? Or update google play services manually by apk? But which version?

Nothing

Hi there,
i got this device brand new, but had this issue out the box, i've already did a factory reset (by settings).
How can i solve this problem?