My airline still requires us to carry out practice autolands. Yes I know a lot of other companies have stopped this including Denti's mob. But I can report from years of trying it in Munich, that it is a hopeless place to practice as the autopilot more often than not trips out on the 737 when the runway is unprotected.
Combine this with very professional but at times sporty sequencing from the tower and I am not at all surprised by the interference with the signal. Interestingly the report says that the 777's autopilot remained engaged, but steered off to the left. Another question is why the go-around did not happen as the captain says he intended. It is in any case a cautionary tale about autolanding without protection.