one soldier is occupying the fortifications/watchtowers/etc but then no more soldiers will go and fortify them further. they all stay in the hq. even if i try to force them out they walk out then back into the hq. my priorities are set to outlying regions and everything.

problem solved. when i restarted the program they moved.

sometimes i have experienced the same bug.
it seems like the missing soldiers are somehow distracted from the scheduled routine...

There is a menu where you can specify how many soldiers you want to protect your borders (this is usually maxed, meaning the border forts will be full), the interior, and the very center of your lands (this is usually set low, which means there will usually be only 1 soldier per building).

(Don't remember exactly how you open that menu, but it's next to the buttons for goods priority, tools production, etc...)