Why can't debian start with systemd?

Question

linux

there is a debian stable, with some packages from testing
After installing fail2ban from testing, he pulled up a new systemd,
respectively, the system now does not boot from systemd, swearing
a start job is running for ifup wlan0
hangs forever, not turning on and off At the same time, in sysvinit mode loads fine, but combinations with fn to decrease / increase screen brightness do not work

Answer 1

Demolished the system, put it out of the stable. The system boots fine, but fn for the screen never worked. (for volume, they both worked and work in all modes)