Issue on the SCR model

[Bryan_Lieblick]

This behavior is expected. From the component mask “The thyristor closes upon a positive voltage between anode and cathode and a non-zero gate signal. It opens when the current tries to reverse.” and in the component documentation “The switch remains closed until the current becomes negative.”. With S1 open note there is a positive voltage across the thyristor. In your circuit the current will never reverse and the thyristor will remain closed.