It was discovered that one of their editors help a manga author try to cover up some pretty heinous cases of sexual assault, and when it got exposed, even went to the point of helping him hide his identity from the rest of MangaOne staff, in order to get him hired again to start a new series. A lot of creators pulled their work from the platform, and several who are published primarily through it also put their series on hold to figure out how best to proceed, since there was a breakdown of trust with the editorial staff.
And THEN it got worse and turned out that MangaOne had also hired Tatsuya Matsuki (creator of Act Age) also under a new pseudonym (though MangaOne has claimed that that wasn't covered up, and staff were aware of this). This made fewer waves for various reasons, but still left editorial staff in the lurch, untrusted by a lot of the creators, and Shogakukan (the publishing company) has hired a third-party law firm to fully audit things and make sure there isn't more nasty stuff going on.
Nanao was one of the artists who put the series on hold out of concern the platform might be going under, but right now, things are kinda...stabilizing again, and Nanao's own editor was (apparently, according to another artist) not the one who was the source of all the trouble, so though he weighed going to a self-published platform, or even dropping the series and starting something new (apparently, he's had ideas!), he's decided to resume the series and see it to its completion.