System.ObjectDisposedException: Cannot access a disposed object, ASP.NET Core 3.1

I am writing an API using SignalR in ASP.NET Core 3.1. I am totally new to .NET Core, and am pretty new to SignalR too. I am having an issue executing MongoDB (Atlas) queries which are running in transactions. It appears that the transaction sessions are expiring before the queries are executing. I’m quite sure it’s a async/await issue, but don’t seem to be able to fix it.