My customers are getting weird/toxic backlinks out of nowhere

Two of my customers have gained toxic backlinks that I know for sure they have not acquired themselves. First I thought that previous freelancer bought those links but when I saw same links appearing to my other customer as well I started to think there is something weird going on.

Those links are SEO directories, such as seohelperdirectory.com, topdomaindirectory.com etc.

Any idea what is happening there? And should i disavow those links?