Reprodusible on unstable/sid, hostapd 2:2.10-24+b1 amd64. Original description contents working solution(After=sys-subsystem-net-devices-%i.device).
Also consider to remove After=network.target, because it breaks wlan link bridging by systemd-networkd, which have Before=network.target and see link in non-ap mode on boot(yes, there is bridge=<brlink> in hostapd.conf, but this not seems as good solution). It's just more important than After=sys-subsystem-net-devices-%i.device, because I can add extra dependency via [email protected]/override.conf, but can't remove already existing dependency this way and need override whole .service file.
By the way, [email protected] have no such problems:
After=sys-subsystem-net-devices-%i.device
Before=network.target
