They have been found to have been altering the contents of the archived articles.
They have DDoSed a server using our browsers when we visit their site
Wikipedia has blacklisted it
It's DNS is banned widely
Guidance published ... asked editors to help remove and replace links to the following domain names used by the archive site: archive.today, archive.is, archive.ph, archive.fo, archive.li, archive.md, and archive.vn. The guidance says editors can remove Archive.today links when the original source is still online and has identical content;
Recommended alternatives include:
Internet Archive
Ghostarchive
Megalodon
The Wikipedia guidance points out that the Internet Archive and its website, Archive.org, are “uninvolved with and entirely separate from archive.today.” The Internet Archive is a nonprofit based in the US.
It's a bit sad, because archive.org is unable to capture some websites that archive.is is able to.
So you either get an imperfect host that is able to capture it (with a dubious integrity record), or you have a void where some stuff cannot be archived and you end up with a void.