The transcode report on Special:Transcode_statistics (formerly Special:TimedMediaHandler) is really slow to load on Commons; I think it's doing at least a full table scan of the transcode table, which has over 5 million rows on Commons.
Additionally this report often cuts off the data and is hard to sort/read through. It needs some love and reworking to make it easier when managing transcode queue stuff!
Might need to add appropriate indexes to transcode table, might just need to make it read it more sensibly.