The driver does not throw an exception on StartTransaction when connecting to a Standalone or Unknown node. This is connected to CSHARP-2561 where the check was introduced.

However, the check misses these two scenarios. This results in an exception being thrown at a later stage when transaction operations are being executed. 

Note 2020-04-20: It is not necessary to check for Unknown because in that case the server is also disconnected and we filter out disconnected servers before checking server type.