The GameProjectUtils::InsertFeaturePacksIntoINIFile() function is not creating a valid entry in the DefaultGame.ini file. It is currently missing a double-quote at the end of the PackSource value for each Feature Pack.
The InsertPack entry for the Starter Content is incorrect. It is missing a second double-quote for the PackSource value. InsertPack=(PackSource="StarterContent.upack,PackName="StarterContent")
The Starter Content entry correctly has a second double-quote for the PackSource value.
There's no existing public thread on this issue, so head over to Questions & Answers just mention UE-65050 in the post.