Sorry,
It would do no good to send me server dumps.
I have not seen a windows os since xp.
I just run a linux server w/2 arma2's and 2 arma3's (dimrod servers),
Just trying to tell how I overcame this problem, (Arma3 servers been running for 6 hours now) since Arma3 update yesterday,
and maybe will give the arma people a place to look for a problem, and hoping something like that to fix windows server.
Sorry I cant be more help,

Just did a temp workaround and works for me so far,

Went in as root and set file permissions to 666 so anyone can read and write to file -> "/tmp/a3_cache_ch.lck"
Now user1 and user2 games can run at same time.
I have no idea where the windows (tmp) file would be located or how to change file permissions and do not know if will create more problems with two users accessing the same file.
But there it is.

Same thing happens with Linux dedicated server
user1 starts an Arma3 game and user2 cannot start Arma3 game
The armaserver file creates a "/tmp/a3_cache_ch.lck" file owned by user1
If user1 stops the arma3 server, the file is not deleted and user2 server never starts up but it keeps trying and the log file keeps growing. Mine was several gig in size before I seen what was happening, (if not have noticed it would have crashed the server when the HDD filled up).
user2 cannot delete the file because it is owned by user1 so user2/arma3server never starts but the log file keeps growing,
and we cannot have two servers running on the same machine.
I dont know if this helps but here it is.