I would think the plugs are not the issue since your charger is not having a problem with one pack but...

Just for the heck of it, if your using banana plugs, see if you can spread out the cage a little to get a better contact. I use solid bullets on my charge leads, the PowerLab charger does not like the bird cage plugs. False readings or something and it sporadically will not charge with the bird cage plugs.

Just a thought to try out, 1.5v & 5v sounds like a bad read. Can't see a cell getting that low or high in voltage. You balance charge right?