Went to dump a list of active modules used by Apache, sudo apachectl -M, and got an unexpected message:

AH01574: module php7_module is already loaded, skipping

A quick scan for php mentions, fgrep -ir php /etc/apache*, resulted in discovering the system had several configuration versions available, something than an apt upgrade most likely grabbed for me.

This was confirmed by ls -l /etc/apache*/mods-available/*php*.

Looking at which modules were enabled, ls -l /etc/apache*/enabled/*php*, confirmed I had more than one.

lrwxrwxrwx 1 root root 29 Nov  4  2017 php7.1.conf -> ../mods-available/php7.1.conf
lrwxrwxrwx 1 root root 29 Nov  4  2017 php7.1.load -> ../mods-available/php7.1.load
lrwxrwxrwx 1 root root 29 May 28 06:40 php7.4.conf -> ../mods-available/php7.4.conf
lrwxrwxrwx 1 root root 29 May 28 06:40 php7.4.load -> ../mods-available/php7.4.load

At this point, it was merely a matter of removing the symbolic links to the older versions and restarting apache.

sudo unlink /etc/apache2/enabled/php7.1.conf
sudo unlink /etc/apache2/enabled/php7.1.load
sudo apachectl restart