Error session_start(): Failed to read session data: redis PHP / Redis

I am using PHP (7.2.30) with Redis as the session handler. Everything works great, sessions are saved to Redis, but rarely I will see the following error:

Error session_start(): Failed to read session data: redis (path: example.com:6379)

I am using PHPs built in session handling as follows.

session_start();
$_SESSION['something'] = 'value';

Any advice on how to track down the cause?