We're experiencing a problem with UnityWebRequest in case when DNS can't resolve domain name given in url.
If we can't connect on some domain name then we connect on the specific ip address. But if ~10 UnityWebRequests which can't be resolved in DNS were created and aborted then any other requests will be completed with a huge lag ~ 20 seconds.

To reproduce:
1. Set DNS to 1.1.1.1
2. Open attached project
3. Play scene
4. See the console output like "Done sec: 20.643974" - it means that simple request was done in 20 seconds

Reproducible: 5.5.0a6, 5.4.0p2, 5.3.6p3, 5.2.5f1