Elevated 406 Errors

We have seen some occasional HTTP 406 error codes on sending emails, but over the last 12 hours or so, the error rates have increased substantially. Is anyone else seeing this?

The response from the call is:

<head><title>406 Not Acceptable</title></head>
<center><h1>406 Not Acceptable</h1></center>

I found a similar issue here from Oct 2020:

and there was a status update: