I got FreeBSD 11 CURRENT too and have the same problem.
Configuring the loader.conf and rc.conf files I get errors and can't get iwn(4) to work.
And the commands on the console just work when I remove the commands from the files.
I just write a script and exec the script after the boot.
That's my temporary solution.
With this solution the driver is very stable. I don't have problems.
Unfortunately I don't have time to explore another solution.
Configuring the loader.conf and rc.conf files I get errors and can't get iwn(4) to work.
And the commands on the console just work when I remove the commands from the files.
I just write a script and exec the script after the boot.
That's my temporary solution.
With this solution the driver is very stable. I don't have problems.
Unfortunately I don't have time to explore another solution.