LinkedIn form fills showed zero in GA4 — UTMs were being stripped on the way

The situation

A Legal Tech SaaS was running LinkedIn Lead Gen Forms as their primary top-of-funnel. LinkedIn Campaign Manager showed 120 form submissions per month. GA4 showed zero leads from LinkedIn. HubSpot showed 40. The marketing team couldn't reconcile any of the three numbers.

The problem

LinkedIn Lead Gen Forms redirect to the advertiser's website with UTM parameters. But the redirect was going through the brand's marketing subdomain (go.legaltech.com) which used a URL shortener that stripped all UTM parameters before the final redirect. GA4 received all the LinkedIn traffic as "direct." Additionally, HubSpot form embed on the landing page had a different action URL than the LinkedIn form redirect destination — causing partial HubSpot capture only.

What we did

1. Traced LinkedIn form redirect path — confirmed UTM stripping at go.legaltech.com URL shortener step
2. Rebuilt UTM passthrough: LinkedIn redirect URL → custom landing page that reads UTMs from URL and stores in sessionStorage → carried through to final form submission
3. Alternatively: switched LinkedIn Lead Gen Forms to native LinkedIn forms with Zapier → HubSpot integration to guarantee 100% CRM capture
4. Fixed HubSpot form embed action URL to match the redirect destination
5. Built GA4 + HubSpot reconciliation report in Looker Studio — all three now within 5% of each other

Why it worked

UTM stripping at redirect intermediaries is invisible until you trace every redirect hop. LinkedIn Lead Gen Forms are particularly susceptible because the redirect URL is defined in Campaign Manager and often goes through marketing automation tools, link shorteners, or subdomains that may not pass UTMs. The fix requires either controlled UTM passthrough or bypassing the web redirect entirely via native LinkedIn form + CRM webhook.