Light leaks

I started film photography again since last year. Had fantastic results with the Kodak Colorplus 200. I use a canon ae-1P. Last month i got the cinestill400D and forgot to change the ISO from 200 to 400. I was told it could be serendipitous as it was a very dynamic film. Some of the shots turned out great, but many others also have significant light leaks in them.

Is this because of pushing a stop, or is something starting to get wrong with the camera ?

Thank you