Thanks @Plfeenstra,
From the looks of it your USB-WIFI connection is being managed by NetworkManager, but only when you are logged on!
Before you login, systemd has already failed to mount the share, as on the one hand it thinks you are online ("Reached target Network is Online"), but Network Manager seems to need time to think and/or who-knows-what that it only manages to connect when you are logged on.
I don't know much about Network Manager, and I would not recommend it for computers that are always online. All you need is wpa_supplicant and systemd-networkd. Oddly, https://wiki.debian.org/WiFi/HowToUse does not even care to explain how to use networkd.
Here (https://hackaday.io/project/162164/instructions) it is more or less well-explained. Let me know if you have problems.