First off, you can remove the copper strip and bend it back, then replace it. They should contact both axles. Next, make SURE the rollers are both connected, if a wire is broken off one, that will cause the issue.
A big help here is a multimeter, you should really have one of those for working around model trains.
Another thing to do is clean the rollers, they're the prime suspects as you have three of the four wheelsets still in contact with the rails.
