Color laser printer darkening long edge of sheets

[aab1]

Sometimes my color laser printer makes prints where the long edge on one side of the paper is darkened. This has happened more than once and a new cartridge solves the issue. But what exactly would be causing this?

I am using compatible cartridges since I refuse to pay $700 for 2800 pages at 5% coverage when compatibles are $150 plus I can normally refill them 2-3 times before the fail. However this time it happened on the cartridge's original toner, but I got them from another supplier.

Thanks