So you may have to look at how the link is working... If the anchor tag has been coded with rel="noopener noreferrer" then this is a directive to not pass any referral data, which will result in anyone using those links to be treated like Direct Traffic.
Some applications like WordPress add this to links that open in new tabs automatically, you can turn that off if you choose, but that might have other impacts to external links that you might want to have those directives.... if you have the ability, and your users are savvy enough, you could potentially give them the option to add or not add directives like that based on their usage... Or just make sure to add UTMs to your partner sites links so that proper attribution can be applied if the referral information is being suppressed