Left AirPod working intermittently

I have a first generation AirPods that were working fine for more than 2 years. Now, all of a sudden, the left AirPod started disconnecting frequently. It works perfect for around 10~20 seconds, but it just disconnects and does not show up on the list anywhere. Once I put it back in the case and try it back on, (with the right AirPod still in my ear), it seems to work, but again, after 10~20 seconds it disconnects.

[Re-Titled by Moderator]