Unfortunately this forum, as usual, has not provided me with any help.
The root of the problem was because the SOURCE DB had it's password saved in a format incompatible with PHP7, solution is to resave the password in a format compatible with PHP7. I did not do this, my hoster (Nexcess rocks) did this for me.
This was posted here because this 'community' comes up in google searches and I am certain others need the same help.