Since V2 Renku projects don’t have the same mechanism to build images on every commit (mind that the Renku project is no longer closely bound to a specific repository), the migration also creates a new session launcher based on the latest image available for the V1 project.
Before turning off the V1 sessions, you could rebuild the image from the session tab. Now, the quickest way is to go into the GitLab project’s page and go into the “Jobs” section (E.G: Jobs · BA_MATH_GEN-16 / ET_data · GitLab ) and manually re-run the last job to create the image.
Mind that it might still fail for other reasons – E.G. you recently posted this problem.