I've also recently experienced loss of edit points for "hiding" commercials on RW disks. ( DVDR 75 )
What seems to work for me is to make another short recording at the end, then
erase that recording, then reapply the "make edits compatible" command.
So far it has restored all the formerly lost edit points.
Maybe the pointer to the "edit point info" gets temporarily "lost" ?
Hope that helps