Because of these issues with site accessibility, a lot of these hentai comic hosting websites should consider having some form of a
backup and migration feature. In that, they could set up integrations between other similar hentai comic hosting sites, so users can always backup and migrate the existing bookmarks they have on one site to another one. Then, in a worst-case scenario outcome, the user does not have to worry about losing all of the content they have saved on one platform.
From personal experience, I tend to use
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a lot more than exhentai, and I've never really run into issues concerning site accessibility with nhentai before. Only on a number of occasions where updates and regular maintenance closed the site's servers for a few hours. But apart from that (iirc) nothing too major, like a database leak or forums crashing.