We’ve found a way to fix that.
On LoginCallback.ashx.cs we put the line below before calling the
ServicePointManager.SecurityProtocol = SecurityProtocolType.Ssl3 | SecurityProtocolType.Tls | SecurityProtocolType.Tls11 | SecurityProtocolType.Tls12;
Then it solved the issue. But our system was down for some time because of it and I wasn’t understanding the reason.
I’ll leave it here so it may help someone else as well. But I think it was strange that I didn’t receive any notification on my auth0 notifications panel.