I see this from time to time. All of the students in my lab, with few exceptions (and it never happens to them) are beginners, and they go in there, close the door, and sometimes they don't come out for a fairly long time. We wonder what is going on. this is when it happens.
We have a small crack under the loading room door. Invariably, when we see this and begin asking questions, we find that the student lost the film, and it jumped down to the floor right in front of that small crack.
In order for the holes and edges to be sharp, the source has to be very small, approaching a pinhole. So, that's what you would be looking for, a very small light source, probably dropped film, fumbling, trouble with not having practiced getting the film on the spool with the eyes closed enough before going in for real. Get down on the floor with the lights out and look for that hole. It WILL be there.
We keep a small teddy bear in the loading room for reassurance. It works quite well. We got more of this kind of stuff before we got the bear. Try Goodwill. Just a couple of bucks.
The other problem we frequently have (this isn't your issue) is when the student forgets the black tube in the Paterson tanks.
By the way, the Paterson tank system is brilliant, but not without fault. I believe it is included in the MOMA design collection, because it is so well designed. It is made entirely of black plastic except for the red band at the top. When a student freaks out in the dark and needs to come out for help, usually what happens is that the opened film goes in the tank WITHOUT THE FUNNEL AND TUBE and the black lid goes on. The door is opened, and the film is fogged. The red ring floods the inside of the tank with red light.
Had they designed the tank with either 1) a black ring or 2) a clear top, this wouldn't happen. One older student got interested in this and called the distributor with the question: Why?? When the answer came back, yes, you guessed it. The ring is red because it looks pretty.
The committee that put it in the MOMA collection DID NOT INCLUDE a basic photo instructor!