I'm don't know why it's unloading but you could try this.
You can have it reload the .dll everytime you open a new drawings.
(DEFUN S::startup ()
(command "netload" "myPath/file.dll")
)
put this in a lisp file add it to the startup.
tools > load application > contents
---------------------------
(defun botsbuildbots() (botsbuildbots))