Thank you, d00p.
As far as I understand the code, this would have been only visible, had I already set "enabled_ownvhost" by the time, the frontend was working.
But as I told you in an earlier post, I added this after I couldn't access Froxlor anymore, directly in the database. So for me, it was indeed missing.
I checked the database - use_mod_proxy is already set to 1, the same goes for vhost_container in ipsandports. You pointed me in the right direction however, as ne next step in the guide (also only visible after "enabled_vhost" was set) was the one missing for me -> a2dismod php7.0
After I did this, restarted apache and reran the cronjob, the missing php-fpm socket was created and I could access Froxlor again ?
What's left are some errors, that appeared after logging in. They seem to be a permission problem in the course of session handling:
On the top (after logging in)
PHP warning/error
#2 session_start(): open(/var/customers/tmp/froxlor.panel//sess_8ca3f6ea8d0350843a5351b4530f0eb0, O_RDWR) failed: Permission denied (13)
/lib/init.php:216
On the bottom
PHP warning/error
#2 Unknown: open(/var/customers/tmp/froxlor.panel//sess_8ca3f6ea8d0350843a5351b4530f0eb0, O_RDWR) failed: Permission denied (13)
Unknown:0
PHP warning/error
#2 Unknown: Failed to write session data (files). Please verify that the current setting of session.save_path is correct (/var/customers/tmp/froxlor.panel/)
Unknown:0
So, any (hopefully) final clue?