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.

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

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

Ugh, now I have to migrate my Tachiyomi subscriptions again