There is a lot of legal troubles for manga piracy recently. Lots of manga and chapters got taken down. So this is probably the reason (but maybe not).

As people said, the site was “DMCA purged” and lost part of its gallery, which, unfortunately, makes it one of the worst manga sites to read online nowadays, which is a shame I always visited it, but now all that’s left is just a hollow body of what it once was.

Mangadex got a DMCA notice recently, which resulted in a huge takedown. Something like 25% of their chapters I read somewhere.

Have fun: https://cubari.moe/read/gist/Z2lzdC9mdW5reWhpcHBvLzcxMjRhZjUyMWExMDU5NDVhNGRmNmEzMzFjOWZjZTU5L3Jhdy9vcG0td2MuanNvbg/

Edit: https://www.reddit.com/r/OnePunchMan/wiki/faq/