mail filter rules page broken

Going to Settings -> Mail -> Filter Rules results in an empty page.

Going to Inspect -> Networking in Chrome shows a network request to https://connect.xfinity.com/appsuite/api/mailfilter/v2 failing after ~30 seconds:

{
  "error": "An error occurred inside the server which prevented it from fulfilling the request.",
  "error_params": [
    "imap-east.ge.xfinity.com",
    4190
  ],
  "categories": "ERROR",
  "category": 8,
  "code": "MAIL_FILTER-0014",
  "error_id": "<redacted>",
  "error_desc": "Error in low level connection to sieve server imap-east.ge.xfinity.com at port 4190"
}