I've not used a Jobo CPP but perhaps the tank was opened briefly fogging the film? The pattern of marks looks like a projection of the film reel onto the film. Perhaps this was done whilst there was liquid in the tank - hence the abrupt cut off.
The only way to solve an issue like this is to repeat it. Just make a single exposure and take it all the way through the process and see if you get the same marks. If you don't it was a one off.
[Total aside: I would be reluctant to use a big machine like a Jobo CPP with students for black and white. The complexity may cause more trouble than it is worth. (Totally needed for colour though). The best 4x5 B&W solution I've found is the Stearman Press tank. It is depressing for a student to make 6 large format exposures and have none of them work out. She should have discovered the error on the first one. That is the advantage or working with sheet film. You can adjust dev for each exposure.]