It seems that at least jbond and I get that error, from firefox:
curl 'https://horizon.wikimedia.org/project/instances/79091983-20ae-44a5-a180-f21ac6663959/?tab=instance_details__interfaces' \ -H 'User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Firefox/78.0' \ -H 'Accept: text/html, */*; q=0.01' \ -H 'Accept-Language: en,en-US;q=0.8,es-ES;q=0.5,es;q=0.3' --compressed \ -H 'X-Requested-With: XMLHttpRequest' \ -H 'Connection: keep-alive' \ -H 'Referer: https://horizon.wikimedia.org/project/instances/79091983-20ae-44a5-a180-f21ac6663959/' \ -H 'Cookie: tabs=%7B%22instance_details%22%3A%22%23instance_details__interfaces%22%7D; WMF-Last-Access=26-Nov-2021; sessionid=REDACTED; GeoIP=FR:ARA:REDACTED:REDACTED:6.08:v4; csrftoken=REDACTED; recent_project=puppet-diffs' \ -H 'Pragma: no-cache' \ -H 'Cache-Control: no-cache' \ -H 'TE: Trailers'