This issue has now been fixed and chrome recorded sessions are successfully converting within the web interface.
Posted Jun 12, 2019 - 18:48 CEST
We've identified an issue preventing the v4.0 chrome extension from converting/creating test scripts. As a workaround, please select the option to "download HAR file" and utilize the HAR upload within the webapp to create your test/script. https://app.loadimpact.com/k6/tests/custom/config