I've never had a problem with my ETRs in cold weather but I too have loaded the film backwards so I was exposing the paper backing instead of the film. I think it was the switching between the Bronica and an old folding camera I had. If this was your problem the whole roll would have been blank and not just the odd frame. When was the last time you changed the battery? It could be a case of low battery voltage and dirty contacts. How are the contacts on the lens you are using? They are electronic leaf shutter lenses I believe.