I took a peek at the Reddit discourse over this and my GAWD some of these "fans" sound like lolicons. Page after page of complaints that they're not kawaii enough anymore and complaining that the girls are growing up. It's one thing to not like the music as much anymore (I don't either, personally) but these grown men writing dissertations on why these 18-20 y/o girls should be forced to wear tutus and pigtails even if they don't want to anymore, or complaining that the back up dancers are "too masculine" and "should be replaced with little girls", some of them saying the girls recent costumes "make them look like men" (??? bitch where, they're in dresses LOL)... it's just gross and transparent.
Ngl I lost interest in Babymetal quite awhile ago but whatever is going on with Yui, Amuse are... not handling it well, like at all. Like damn, just be upfront - say she's sick and won't be there, and say it in advance. This never would've blown up if it weren't for Amuse trying to be sly. If I were a diehard fan I'd be afraid to ever buy tickets to a show again since they clearly feel no shame in pretending all members will be present for the sake of ticket sales.