Left lane full, right lane open.

I've experienced this a few times now. The left-most lane will be congested and the right-most will be totally empty. Traffic moving at the same speed so if you want to overtake the only way to do it is in the right-most lane.

Have you experienced this? And why might this be the case?

I know there are some cases where this should be expected: the lanes might soon split into different roads which could cause this, or a lane could be ending, or there could be many cars merging in from the right.

Obviously confusion about the passing lane is an issue, but now it seems there are so many people hogging the passing lane that you can't use it to pass while the right-lane is wide open.