Well, this was a rather strange (and somewhat alarming) bug.
When I just reopened the level I was working on, all the script-related information (shift, warp, trigger, sign) for the last screen I worked on had disappeared! Everything else seems to be intact, thankfully, and it's not too much trouble to put everything back into place, but I KNOW I had to have this information saved because I playtested the level multiple times before closing the level editor earlier today. No idea what happened or why, but it should be all okay!