Frequently facing with the exception (Thread static buffer is already in use)

Hey MongoDB Team.

I’m having an issue on production environment about the following

An error occurred while deserializing the FlowNodeId property of class ContactInputVariable: Thread static buffer is already in use.
The environment usually had a lot of activity and heavy load
One of the potential causes could be hitting allowed max pool size, but was my opinion/understanding and nothing more (I could be wrong).

Class Model

    public class ContactInputVariable
    {
        [BsonId]
        [BsonRepresentation(BsonType.ObjectId)]
        public string Id { get; set; }
        public string ContactId { get; set; }
        public string InputText { get; set; }
        public string VariableName { get; set; }
        public string FlowId { get; set; }
        public string FlowNodeId { get; set; }
        public DateTime Created { get; set; }
    }

Project is using Official .NET driver for MongoDB v. 2.15.1

Have no idea why is this happening.
Could you give me some insight about what might be causing the issue.

Thanks in advance.