There could be several reasons. Maybe the popularity of Berserk led to it being taken down from Manga Rock. Another possibility is that there were legal complications preventing its availability on that particular platform.
It could be that Manga Rock has run into legal troubles and had to remove its manga content. Or, there might be server problems or maintenance going on that's preventing you from finding what you're looking for.
Maybe the app has been shut down or its manga library has been updated and some titles are no longer available.
Maybe Manga Rock doesn't have the license to host Tokyo Ghoul or it could have been removed due to copyright issues.
Manga Rock was shut down due to copyright infringement. So, you won't be able to find One Piece or any other manga there anymore.
Maybe it's because Manga Rock was shut down for copyright infringement. So, you won't be able to link to it.
Sometimes, the app might have been removed from the app store or there could be a problem with the version you're trying to install. Try looking for updates or alternative sources.
It could be that the server is down or there's some technical glitch. You might want to wait a while and try again later. Also, check if your account is still active.
Sometimes it's just a matter of luck. Keep looking, ask for recommendations from friends or online manga communities. You might discover something you love soon.
Maybe you're not looking in the right places. Try different search terms or check popular manga-related platforms.
It could be that Domdomsoft doesn't have the rights to host Overlord manga. Sometimes licensing issues prevent certain content from being on specific platforms. You might want to look on official manga sites or apps.