The error was being thrown at
var response = await _httpClient.PostAsync(url, requestContent);
Essentially the request was timing out. I had a look at the httpClient and it is set to timeout after 5 seconds.
client.Timeout = TimeSpan.FromMilliseconds(5000);It would appear that sometimes a timeout would occur and other times not, hence why it worked before and not now.
For now, I have increased the timeout and I'm getting no more errors.