web-console and processes

Sometimes I see No exception information available in web-console.

Digging in the web-console source finds me this:

If you happen to run on a multi-process server (like Unicorn or Puma) the process this request hit doesn't store %{id} in memory. Consider turning the number of processes/workers to one (1) or using a different server in development.

So I look at my config/puma.rb, change it and never see this error message again.