FS2014 duplicate entry '.cctor' in method table #18767

1>FSC : error FS2014: A problem occurred writing the binary 'G:\coldfar_py\sharftrade9\Libs5\KServer\fstring\obj\Release\netstandard2.0\PersistedConcurrentSortedList.dll': Error in pass2 for type PersistedConcurrentSortedList.Type.fCell2`1, error: duplicate entry '.cctor' in method table
1>Done building project "PersistedConcurrentSortedList.fsproj" -- FAILED.
1>FSC : error FS2014: A problem occurred writing the binary 'G:\coldfar_py\sharftrade9\Libs5\KServer\fstring\obj\Release\net9.0\PersistedConcurrentSortedList.dll': Error in pass2 for type PersistedConcurrentSortedList.Type.fCell2`1, error: duplicate entry '.cctor' in method table
1>Done building project "PersistedConcurrentSortedList.fsproj" -- FAILED.

[<ProtoBuf.ProtoContract>]
type fCell2<'CellTupleKey when 'CellTupleKey: comparison> =
| B of bool
| S of string
| D of decimal
| A of fCell2<'CellTupleKey> []
| T of 'CellTupleKey * fCell2<'CellTupleKey>
| N 
    member this.toJsonString() =
        let rec toJson (f: fCell2<'CellTupleKey>) =
            match f with
            | S s -> sprintf "%s" s
            | D d -> sprintf "%f" d
            | A arr -> 
                let elements = arr |> Array.map toJson |> String.concat ", "
                sprintf "[%s]" elements
            | T (key, value) ->
                let keyStr = sprintf "%A" key
                let valueStr = toJson value
                sprintf "%A: %s" keyStr valueStr
        toJson this

    static member compareArrays (arr1: fCell2<'CellTupleKey> array) (arr2: fCell2<'CellTupleKey> array): int =
        Seq.zip arr1 arr2
        |> Seq.tryPick (fun (x, y) ->
            let res = compare x y
            if res = 0 then None else Some res)
        |> Option.defaultValue 0

    static member compareLength (arr1: fCell2<'CellTupleKey> array) (arr2: fCell2<'CellTupleKey> array): int =
        let a1l = if arr1 = null then 0 else arr1.Length
        let a2l = if arr2 = null then 0 else arr2.Length
        compare a1l a2l

    static member Compare (x: fCell2<'CellTupleKey>, y: fCell2<'CellTupleKey>): int =
        match box x, box y with
        | null, null -> 0
        | _, null -> 
            if x = S null then 0 else 1
        | null, _ ->
            if y = S null then 0 else -1
        | _ ->
            match (x, y) with
            | (D d1, D d2) -> Decimal.Compare(d1, d2)
            | (S s1, S s2) -> String.Compare(s1, s2, StringComparison.OrdinalIgnoreCase)
            | (A arr1, A arr2) ->
                let lenComp = fCell2.compareLength arr1 arr2
                if lenComp <> 0 then lenComp
                else fCell2.compareArrays arr1 arr2
            | (T (tag1, f1), T (tag2, f2)) ->
                let tagComp = compare tag1 tag2
                if tagComp <> 0 then tagComp
                else fCell2.Compare(f1, f2)
            | (D _, _) -> -1
            | (_, D _) -> 1
            | (S _, (A _ | T _)) -> -1
            | ((A _ | T _), S _) -> 1
            | (A _, T _) -> -1
            | (T _, A _) -> 1

    interface IComparer<fCell2<'CellTupleKey>> with
        override this.Compare(x: fCell2<'CellTupleKey>, y: fCell2<'CellTupleKey>): int =
            fCell2.Compare(x, y)

| N of unit