Hi Enrique,
Maybe the OnApplicationReady is not the better place to use a TenantSwitch action.
Since it is a Client Action, what can be happening is that it is loading the Module before doing the first permissions check and initiating your session.
Not sure if this action runs before or after your server session is initiated.
But if it happens before, when your session initiates there is a risk that you go to you default tenant again.
If possible try to place the switch tenant action in your login logic.