Short answer
Usually one of: the linking page or site was taken down or redesigned, the linking site removed the link deliberately, the linking domain itself went offline or was deindexed, or a redirect/URL change on your own site broke what used to be a working link target.
The single most common cause is mundane: the page that linked to you was deleted, moved, or the whole site was redesigned without preserving old URLs. Illumae's backlink checker shows your current backlink profile, so you can compare it against an earlier snapshot to see which specific links disappeared and investigate each one directly.
If a link pointed at a specific page on your own site and that page's URL changed (or the page was deleted) without a redirect in place, the link technically still exists on the other site but no longer resolves — which some backlink tools count as lost even though the fix is entirely on your end. Auditing your own site for broken internal structure and missing redirects after any URL changes is worth doing proactively.
Sites do sometimes deliberately remove outbound links — during a content refresh, a shift in editorial policy, or after a manual review of their own outbound link profile. If a specific relationship mattered to you, a polite direct outreach asking about it is sometimes worth trying, though there's no guarantee of restoration.
A domain that expired, was deindexed by Google, or simply went offline takes every backlink it gave you with it, through no action on your part at all. This is unfixable from your side beyond simply no longer counting that link, but worth confirming so you don't spend time chasing a dead end.
Backlink-tracking tools crawl the web on their own schedule and can show minor day-to-day fluctuation from re-crawling timing rather than genuine link loss — a real trend over weeks is more meaningful than a single day's snapshot. backlink checker shows spam-risk banding alongside authority, which also helps separate a low-value link's disappearance (rarely worth worrying about) from a genuinely valuable one going missing.
Generally no, and in some cases losing a spammy link is actively good for your profile. Focus attention on losses among your higher-authority, low-spam-risk links, which are the ones actually contributing meaningfully to your site's authority.
Sometimes, by contacting the site directly and asking, but there's no guarantee and no tool (including Illumae) can force it. It's often more productive to focus effort on earning new links than chasing every lost one.
It shouldn't, if the redirect is set up correctly (a proper 301 from the old URL to the new one) — most backlink tools and Google itself will follow the redirect and still credit the link. It's worth explicitly checking that any URL changes you made include working redirects, since a missed one genuinely does break the link.
Illumae's backlink checker shows your current profile with authority and spam-risk data whenever you check it, which you can compare against a previous check to spot changes, but it doesn't currently send automated real-time alerts the moment a specific link disappears.
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