I do not use Jenkins, but the problem that occurred to me was that I used the Fabric Mac application to apply the API key through the setup process.
For me, the fix was simple:
Go to fabric.io category → Organizations → Your API → API
and replace this:
Fabric.with([Crashlytics.self])
by:
Fabric.with([Crashlytics.start(withAPIKey: "YOUR_API_KEY")]
Fabric API. , Jenkins , Fabric , , API.