Trending topics have shifted. Allegedly they removed some manually-curated trending system that was previously in place, which may have been a system that worked well for some demographics but wasn't working great for Japan.

That is mildly surprising. I would have assumed a manual process would have done a better job of adapting to different languages and cultures than an automated process unless that manual work was done by people outside that cultural context.

I hear that they were manually pushing political tweets which I guess Japan doesn't hate engage with as much as people in the west do.