Sometime the client can't connecte to server even if the MqttConnectionValidate method finished

### Describe your question
I tested the client(using the MQTTX) and the server revently. The client can't connecte the server without any error _**sometimes**_, and When I test the Broker with breakpoint, I found that the MqttConnectionValidate method have finished and execute the code 'c.ReasonCode = MqttConnectReasonCode.Success;' in fact. I'm not sure the probem is a bug or a usage mistake.

### Which project is your question related to?

- Server

### Part of My Code

Start by reproducing the intermittent connection failure with MQTTX and inspect the server flow around MqttConnectionValidate and the assignment of MqttConnectReasonCode.Success. The issue names no source file or test, so first identify the relevant connection-handling entry point and add or run a reproduction before determining what done means.

Written by the indexing model from the issue text.