SqlCommand Time Out After Repeat (Simple) Queries in .NET / F#

I am running a relatively simple query using SqlConnection / SqlCommand / SqlDataReader. The code looks like the below. I have this inside of a function where I pass in a date to call this function, that executes this query.

The odd thing is that the first time the function is run, it's fast. The second time, it's fast too, but on the third time it gets stuck for ~20 seconds and sometimes longer, causing a time out. In SSMS, the same query is quite quick and never lasts longer than ~1 second.

Any suggestions of what might be casuing this?

let conString = "..."    
use connection = new SqlConnection(conString)
connection.Open()
        
let qry = "  SELECT Date, Col1 FROM myTable
                        WHERE 
                        Date = @myDate"
        
use command = new SqlCommand(qry, connection)
        
command.Parameters.AddWithValue("@myDate", startDate) |> ignore
        
use reader = command.ExecuteReader()
while reader.Read() do 
   Console.WriteLine(reader.GetDateTime(0).ToShortDateString())
sw.Close()