Comparing two local profiles broken

If I go to https://profiler.firefox.com/compare/calltree/?globalTrackOrder=0w2&profiles[]=https%3A%2F%2Fprofiler.firefox.com%2Ffrom-url%2Fhttp%253A%252F%252F127.0.0.1%253A3001%252F30ks3vh7155clhscmnhysv7qx9pz2pjifjnc7ir%252Fprofile.json%2Fcalltree%2F%3FglobalTrackOrder%3D10%26hiddenGlobalTracks%3D0%26symbolServer%3Dhttp%253A%252F%252F127.0.0.1%253A3001%252F30ks3vh7155clhscmnhysv7qx9pz2pjifjnc7ir%26thread%3D1%26v%3D12&profiles[]=https%3A%2F%2Fprofiler.firefox.com%2Ffrom-url%2Fhttp%253A%252F%252F127.0.0.1%253A3000%252F2mk18fhilj68xqi2nybaw2vbx2v9xbjnyzcn66n%252Fprofile.json%2Fcalltree%2F%3FglobalTrackOrder%3D10%26hiddenGlobalTracks%3D0%26symbolServer%3Dhttp%253A%252F%252F127.0.0.1%253A3000%252F2mk18fhilj68xqi2nybaw2vbx2v9xbjnyzcn66n%26thread%3D1%26v%3D12&thread=2&timelineType=category&v=12, firefox profiler says `The call tree is empty for “Diff between 1 and 2”` and shows the pid of the process recorded in the second profile in both tracks.

┆Issue is synchronized with this [Jira Task](https://mozilla-hub.atlassian.net/browse/FP-970)