Installation of SQL Server Express LocalDB 2017
LocalDB is a quirky flavor of SQL Server. In most cases, unless there's specific functionality in LocalDB that you need, I'd suggest running the "regular" Express Edition--as you can avoid quirks like the one you're running into. Additional details of differences are included in this article.

LocalDB has an "automatic" instance that is tied to current user. To connect to that instance, you would use a connection string like "Server=(localdb)\MSSQLLocalDB;Integrated Security=true". 

You can also create an explicitly named instance using the SQLLocalDB.exe command line utility. Depending on your installed version, the path may vary (in this example, 130 is SQL Server 2016, but you would use 140 for 2017, etc):

C:\&gt; cd "C:\Program Files\Microsoft SQL Server\130\Tools\Binn"
C:\&gt; SqlLocalDB.exe create MyLocalDB
C:\&gt; SqlLocalDB.exe start MyLocalDB


The SQLLocalDB info command can be used at any time to determine the state of an instance, whether it is running or not:

C:\&gt; SqlLocalDB.exe info MyLocalDB


Additional info on creating &amp; connecting to a LocalDB instance can be found on docs.microsoft.com.