Issue
You're seeing the error ERR max number of clients reached and running out of connections.
Resolution
There are several things you can do to avoid this, such as using a connection pooler to reduce the number of connections, setting an appropriate connection timeout to close inappropriate idle connections.
Here is a blog post, talking about above things, and also many useful tips. Please check it out!
https://blog.heroku.com/real-world-redis-tips