From Xero:
We believe the root cause has been addressed, we will continue monitoring the situation. Thank you for your patience

From Xero:

Although the latency seems to have dropped back down to normal levels, we're still working to identify and correct the root cause of the problem. We will keep you updated.

For further updates please see https://status.developer.xero.com/

This issue has been re-opened please see the note from Xero below

From Xero:
Sadly the API is partially unavailable again. Our apologies for this, the team are investigating and trying to identify the root cause.

For further updates please see https://status.developer.xero.com/