These are my thoughts:
DSP is to blame. They debuted Hyunjoo in a group when she wanted to be an actress and stuck her very young in a group of very young highschool aged girls. Unlike Hyunjoo, the other members genuinely wanted to be singers. They got frustrated when they felt she wasn't putting in the same amount of work they were. This lead to Hyunjoo being isolated for the rest of her time as a member. They both got more and more upset with each other and the members did not know/care about her mental health. They probably talked about her behind her back, excluded her from things, gave her the cold shoulder, and snapped at her for every little thing she did "wrong." Hyunjoo is kinda a shy person and didn't develop social skills to deal with their attitude so she never stood up for herself and let them attack her, maybe even believing what they said to a degree. That's why she went on The Unit, not because she wanted to be a singer, but to prove that she was capable to the members and to herself. Speaking of the Unit, it's clear they didn't get along cause when Hyunjoo competed none of the members supported her. April were her labelmates and couldn't show up to the finale? Jseph from KARD supported her. Even Hellovenus, who hadn't promoted with Yoonjoo in 4 years and continued with a different lineup for most of their career managed to support her and show up to the finale. 100% Hyunjoo and April didn't get along.
The instances of the tumbler, the shoes, that's roommate bullshit tbh. Roommates take eachother's thing all the time and sometimes its really annoying but it's also not the end of the world. As for the inconsistencies, I blame DSP yet again. They're telling these girls what to say and can't stick to one narrative and while desperately coming up with "evidence," they aren't fact-checking themselves. If they were really saying how they felt, stories from Somin would come up, but somehow they haven't. That's because DSP is trying to distance Somin from this controversy as much as possible. For some reason DSP doesn't want to say the simple truth "the girls did not get along" probably because that would make the April members take the blame, at least partially. They're trying to make the April members out as the victims because they think that is the only way to save their career. Thing is, that's not the truth, so their narratives are all over the place. Also, provably lying just digs their graves even further and makes them seem more untrustworthy. If they went to Hyunjoo in private to work things out and made a statement saying they talked to her, they probably could have survived this scandal. Yeah people would say "they just did it to save their careers." That is probably true, but it wouldn't have been dragged out for months caught up in lies. And if Hyunjoo made a statement vaguely forgiving them, they could have moved on from this. That would mean they would have to genuinely apologize though, but I think all the girls have matured since then and probably would have at least listened to her and acknowledged where she is coming from and then either apologized or provided their perspective. That's how adults deal with these things, but DSP didn't go the mature route, they went the cowardly route.
I feel bad for all the girls involved. Rachel and Chaekyung are having their careers stripped away and they didn't even do anything. Chaekyung (my bias) has been working hard for a really long time and April was the fourth group she debuted in. I feel bad for Hyunjoo because I'm sure they weren't nice to her and she probably felt very alone because the company wasn't standing up for her. And I kinda feel bad for the members too because they were young and immature and driven towards a goal as singers. I'm not sure how severe the "bullying" really was, it could be really bad and it also could be not so bad. They might have just said a few things that really hurt Hyunjoo, but didn't realize how sensitive she was. I feel bad because they maybe didn't actually bully and were just working really hard and now their six years of hard work and almost making it big has gone in the blink of an eye. In general these bullying controversies have lots of gray, but netizens view it so black and white. Victim is right and a good person, perpetrators are evil and deserve punishment. I have put a narrative in my mind that makes sense and gives each person a logical point of view. I'm not saying I'm right, but that's just one perspective that not many people are bringing up. What do you think?