During testing, we've seen that upgrades to Stretch from Jessie can have an issue if UWSGI is still left from a previous installation:

apache2: Syntax error on line 146 of /etc/apache2/apache2.conf: Could not open configuration file /etc/apache2/mods-enabled/uwsgi.load: No such file or directory Action 'restart' failed. The Apache error log may have more information. dpkg: error processing package lava-server (--install): subprocess installed post-installation script returned error exit status 1 Setting up lava-server-doc (2017.7-1~bpo9+1) ... Setting up lava-dev (2017.7-1~bpo9+1) ... Processing triggers for systemd (232-25) ... Processing triggers for man-db (2.7.6.1-2) ... Errors were encountered while processing: lava-server

The problem is because of a bug in the uwsgi packages. The uwsgi module is not cleanly removed from apache. Run this command to fix:

$ sudo a2dismod uwsgi

Then complete the install:

$ sudo apt-get -f install

Fresh Stretch installs should not be affected as 2016.12 in Stretch does not use uwsgi.