I was about to update a MassMessage list using https://meta.wikimedia.org/wiki/Special:EditMassMessageList/Meta:Administrators/Mass-message_list. Each time I've tried the result is an Error 500.
Request from <redacted IP> via cp3031 cp3031, Varnish XID 269356886 Error: 500, Internal Server Error at Wed, 31 Jan 2018 10:34:21 GMT
The rest of Special pages I've checked work well.