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).

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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