Number of Processing jobs decreases

I have one server with 20 workers available.
It starts out processing 20 jobs at a time but after a while the number of processing jobs decreases. There are enough Enqueued jobs available but they’re not picked up by the workers.
Eventually the number of processing jobs decreases to 1.

How can I make sure every worker always keeps working as long as there are Enqueued jobs available?

Thanks,
Marc

Anybody have an idea how I could debug this?

Enable logging in your application. That should be able to tell you what’s going on.