If you try to run bot checker net test with 27.5.1 and with proxy set, you may encounter following issues https://imgur.com/Q0gTIdw. Here is how you can fix them:
If "Change WebRTC ip" is set to true, this means that some network activities, which are part of WebRTC protocol will be disabled.
This can be useful for proxies which are not capable of routing UDP traffic, for example all http proxies.
If proxy supports UDP, it would be better to set "Change WebRTC ip" to false. After doing this all WebRTC traffic will be sent through proxy, including UDP.
This can help to resolve external ip in more natural way.
Note that setting "Change WebRTC ip" to false doesn't mean that your real ip will be exposed https://imgur.com/HkuLqzF. In worst case(if you are using http proxy for example), site won't be able to resolve it through WebRTC.
After adjusting proxy settings you will have the following results https://imgur.com/K6ZxOvh
In order to detect proxy, test authors uses interesting technique.
This technique works only in certain circumstances in BAS and not in the way as was originally intended.
That is why if you run test several times, sometimes it may pass, sometimes it may not.
Anyway it is already been fixed, so you need to wait for 27.6.0 update.
Here is the final result: