Lightning charger cable only charges phone when above 40ish %

I recently bought two USB c lightning chargers and they worked perfectly for the first couple weeks. Now they will only charge my phone when it is above about 40 % I’ve even given it 10 minutes to start, (it works just fine if it’s above this percent) the old style charger still works fine no matter what. I’m in the process of getting new cords but I was just wondering if anyone ran into similar issues and had any knowledge as to why this is happening.