They seem to have never came back up since the scheduled maintenance.
EU realms are displaying the "We'll be back soon!" maintenance page, which is kind of odd (maybe it should status nok too?). Never seen the API dump HTML before. =\
Depending on what type of maintenance they use for the site the API can spit out the maintenance HTML page sometimes.
Regardless the EU deploy for 5.2 data is done and the error with US auction data was also fixed so you should be all set now. Let us know if you see other errors.