Almost always one of: missing or incorrect redirects, a changed URL structure without complete mapping, lost internal linking, or broken hreflang and canonical signals — all preventable and all fixable once identified, usually through a proper post-migration audit.
Missing redirects for pages that moved, redirect chains that dilute the signal, or redirects pointing to the wrong destination are the single most common cause, and the easiest to check directly with a crawl of the old URL list.
A changed URL structure without complete mapping, lost internal linking that previously reinforced key pages, or broken hreflang and canonical signals on a multilingual site — see hreflang for pharma websites for how that specific signal commonly breaks.
A crawl comparing the old and new site structure against current indexation, rather than guessing — see SEO migration for the process that should have prevented this, and which we can also run diagnostically after the fact.
Often, yes — correcting missing redirects, restoring lost metadata, and fixing broken internal links after a migration can recover much of the lost visibility, though not always fully or immediately, particularly if pages were deindexed for an extended period. The sooner these issues are identified and corrected, the more of the original ranking signal is typically recoverable.
Once the underlying issues are corrected, a few weeks is typical for search engines to recrawl and reassess the affected pages, though it depends on how long the problem was live and how severely it disrupted indexation. A longer-standing issue generally takes longer to recover from than one caught and fixed within days.
The reliable way is following a structured migration checklist that covers redirects, metadata, and technical signals before the new site goes live, rather than fixing issues reactively afterward. See what is a website migration checklist for the full preventive process, which is considerably less costly than recovering lost traffic after the fact.
The most frequent causes are missing or incorrect redirects from old URLs to new ones, lost metadata like title tags and meta descriptions, and changes to site structure that break internal linking patterns search engines had indexed. Content changes made at the same time as a migration can also make it harder to isolate which change caused the drop.
Tell us when it happened and what changed and we will help you find the actual cause.