'Value cannot be null error casting Generic list to F# List / Array

My Code is ( using Microsoft playwright to scrape a web page )

let bpl = page.Locator("//tr[@title]")
let! links = 
    bpl.EvaluateAllAsync("(tr) => tr.map(element => element.getAttribute(\"title\"))") 
    |> Async.AwaitTask
let aa = links |> Seq.toArray

If I just run the first 2 lines - it will return what looks like a System.Collections.Generic.List of type string - this is exactly what I need.

Now I want to cast to an F# list or array - but as soon as I add the 3rd line I get an error ( Value cannot be null ) . Only the error happens before it even reaches the 3rd line.

what am I missing?

Full stack trace:

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'Value cannot be null error casting Generic list to F# List / Array

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