As reported by @brunolins16 on the FR channel
https://dev.azure.com/dnceng/internal/_build/results?buildId=2069040&view=logs&j=366a1024-3a8a-5d08-6c00-a4b17dce0d38&t=238871f9-7ef2-5729-2537-1315178305fb
As something to try, I updated source-indexer repo to latest; https://dnceng.visualstudio.com/internal/_build/results?buildId=2069141&view=results will publish a version using the latest MsBuild.StructuredLogViewer shortly, but we'll likely need to wait until the actual structured logger repo is updated to support v.15 before this works