took me a while to work out why! - ive since found that if you significantly edit or move the code elsewhere, from its original place/form, this will drop it from the server behaviour list.
my advice, if important/critical, would be to copy the code of a newly made recordset into a text do somewhere and save it.
Should you decide to tinker with the code in place causing it to dissapear, just copy the original back in place.
This works for me.