I've been migrating a number of sites (Drupal 7, 8, Wordpress) from one server running Ubuntu 14.04 and php5 to one running 16.04 and php7. Some of them work right off the bat and some have required some fiddling with.
The one I'm working on right now works fine except it seems to only show Stark. It uses a custom theme based on Bartik 8.4.5.
I've checked file permissions, as that's usually been the first issue: having some of them root that shouldn't be.
Other than that, where are some places I would need to look to see if something is pointing to the wrong location -- or is a migration like this sometimes an impossibility?
What I've done for the migration is import the db and copy all the files over.