Please forget the “preview” mode, this was a hacky way to get raw issues, and only raw issues. With the preview mode, you did not get coverage, duplication, the tracking of issue state over time, issue assignment to the relevant developers, the possibility to quality an issue, the ability to drill down into issue multiple locations, and most importantly the quality gate defined for your project.
GitLab currently only wants to ingest our raw data. It might not bother the few of you who care only about raw issues, but it does bother us because it breaks the overall user experience that we’ve designed for our users and the value proposition that we bring to them. GitHub, Microsoft (with Azure DevOps) and Atlassian (with Bitbucket Cloud) allow us to bring this value to the development teams. Currently, GitLab does not.