Request not sent

I have come across this issue when using an asynchronous request. It seems as though iOS limits the number of open connections to a single domain, such that all subsequent connections fail in the manner you have described.

If connections typically complete quickly, this possibly won't be an issue.

The solution is to limit the number of open connections to the same domain to prevent this from happening.

The answer posted by karlos works because the synchronisity of the connection blocks others from being opened.

In your code your request take default timeout is 60s, but you can change Request time out in your code as below.

in your NetworkItem class change time out.

init(request:NSMutableURLRequest){
    self.request = request
    self.request.timeoutInterval = 120
    super.init()
}

Like mentioned in comments, I had DNSSEC (cache poisoning protection) enabled on my hosting service.

Disabling it, fixed the issue, even though that might not be a really nice solution. After a few weeks of searching, that'll be good enough.

I'll give the bounty to someone that can explain it, or who can provide a better solution.