Setting Picker ItemsSource results in "Object must implement IConvertible." - xamarin.forms

Question

I can't figure out why I'm receiving the following error when setting the ItemsSource property on a picker control:
"Object must implement IConvertible."
XAML
My XAML is as follows:
** Error: "Object must implement IConvertible." **
<Picker ItemsSource="{Binding Roles}" />
What's interesting, is that I can set the ItemsSource property for a listview control with no issues in the same file.
Different control but same ItemsSource binding in same XAML file:
** This works! **
<ListView ItemsSource="{Binding Roles}" />
In conclusion, why do I only receive an exception when setting the ItemsSource for a Picker but not for a ListView control?
Appendix:
//--------------------------------
// Initializing viewmodel instance
//--------------------------------
var viewmodel = new Dashboard(user, _account.Query);
var page = new DashboardPage() { BindingContext = viewmodel };
await viewmodel.LoadAsync();
.
.
.
//---------------------
// Viewmodel definition
//---------------------
type Dashboard(user:AuthenticatedUser, query:Query) =
inherit ViewModelBase()
let mutable name = sprintf "%s %s" user.FirstName user.LastName
let mutable primaryRole = user.Role
let mutable roles = seq []
let mutable role = ""
let mutable positions = seq []
let mutable position = ""
let mutable incidents = seq []
let mutable incident = ""
let mutable accountabilities = seq []
let mutable accountability = ""
member x.Name with get() = name
and set(v) = name <- v
base.NotifyPropertyChanged(<# x.Name #>)
member x.PrimaryRole with get() = primaryRole
and set(v) = primaryRole <- v
base.NotifyPropertyChanged(<# x.PrimaryRole #>)
member x.Roles with get() = roles
and set(v) = roles <- v
base.NotifyPropertyChanged(<# x.Roles #>)
member x.Role with get() = role
and set(v) = role <- v
base.NotifyPropertyChanged(<# x.Role #>)
member x.Positions with get() = positions
and set(v) = positions <- v
base.NotifyPropertyChanged(<# x.Positions #>)
member x.Position with get() = position
and set(v) = position <- v
base.NotifyPropertyChanged(<# x.Position #>)
member x.Incidents with get() = incidents
and set(v) = incidents <- v
base.NotifyPropertyChanged(<# x.Incidents #>)
member x.Incident with get() = incident
and set(v) = incident <- v
base.NotifyPropertyChanged(<# x.Incident #>)
member x.Accountabilities with get() = accountabilities
and set(v) = accountabilities <- v
base.NotifyPropertyChanged(<# x.Accountabilities #>)
member x.Accountability with get() = accountability
and set(v) = accountability <- v
base.NotifyPropertyChanged(<# x.Accountability #>)
member x.LoadAsync() =
async {
do! async {
match! user |> query.Roles with
| Error _ -> failwith "Query for 'roles' failed"
| Ok result -> x.Roles <- result
}
do! async {
match! user |> query.Positions with
| Error _ -> failwith "Query for 'positions' failed"
| Ok result -> x.Positions <- result
}
do! async {
match! user |> query.Incidents with
| Error _ -> failwith "Query for 'incidents' failed"
| Ok result -> x.Incidents <- result
}
do! async {
match! user |> query.Accountabilities with
| Error _ -> failwith "Query for 'accountabilities' failed"
| Ok result -> x.Accountabilities <- result
}
} |> Async.StartAsTask

Answer 1

I had to use an ObservableCollection instead of IEnumerable (i.e. seq).
Note: I'm not sure why ListView worked without this.
let mutable roles = ObservableCollection<string>() // Updated
...
member x.LoadAsync() =
async {
do! async {
match! user |> query.Roles with
| Error _ -> failwith "Query for 'roles' failed"
| Ok result -> x.Roles <- ObservableCollection<string>(result) // Updated
}