After reading the commit I understand it modifies the management so that parallel workers don't count against connection_limit so I don't understand why I experience the problem
Nor do I. Hoping a -hacker responds here, I just wanted to comment about the thread/patch that you mentioned.
What do you mean by "hijacked"?
After David's patch got posted, ending the thread in theory, Peter added a slightly related patch to the thread, "hijacking it" to a new purpose. What likely happened (though I didn't look) is that the new patch was realized to have been misplaced and moved to a new thread, but no one noted that on the old thread and so it looks as if that thread went unresolved if one doesn't read closely and assume that the "I'll commit this tomorrow" actually happened - which it did but no link to the commit was added to the thread.