Did you use the default Ubuntu PPA? OR using your own custom ppa? Thanks!
Repository used is mostly depend on the linux version EE is running. If asked for Ubuntu , we use
http://mirror.aarnet.edu.au/pub/MariaDB/repo/ for Mariadb and
ppa:ondrej for php-fpm .
For nginx we use custom repositories .
Nginx we use OpenSuse repository
I hope your query is resolved. I am closing this support topic for now.
Feel free to create a new support topic if you have any queries further.