Their first anniversary wasn't officially cancelled, the
company tweet just mentioned it was postponed until further notice. Also the longer nothing is either official stated or a leak comes out with actually information, the boring answer is probably legal issues, whether that music producer, a high level anti/death threats or someone broke into Vespers home, ect.
If it was a breach of contract they would have fired one or both of them weeks ago, they have been dealing with things quickly when something happens recently, which I've appreciated about Cover. I also haven't seen Cover being spiteful or purposely malicious yet, regardless of peoples feelings of upper management, so I find it unlikely they've just been mothballed. Plus they probably signed their contracts months before debut so they would already be locked in for at least a another year, maybe more.
Not-Vesper had his stream with Girl-dm on the
10th of May so would be weird for them to suspend him two months late and be so cagey about it... I thought Lando also join one of her streams around the same time, but can't find it. Though still, wouldn't explain why he's also been forced to stop all activities too, if Randon streaming was an issue.
Though people have been rrating all over the place and sometimes I really can't tell if they're serious or just having laugh. At this point might as well just stop looking for info and wait until Cover says something.