One airpod charge bar doesn’t show on my phone

Hi, I have AirPods. They've worked fine for several months. Today one of the AirPods suddenly stopped working. I've already tried to fix it by "forgetting the device" and re-pairing them with my iPhone. I've also turned off my phone and back on. When I re-pair them, the battery bar shows that the case is fully charged, the right AirPod is fully charged, but there isn't a charge status bar for the left AirPod at all. It doesn't show it's half charged, fully charged or anything. There is no charge status bar at all.