The W3C compliance test is currently running much more slowly than usual which is delaying all reports that use this test (e.g. Comprehensive reports). Disabling the W3C compliance test avoids this problem.
The W3C test relies on an external service which we suspect is faulty. We are investigating and hope to have this resolved shortly.
[11:15 GMT] This issue was resolved last night and all systems are back to normal. Thanks for bearing with us.