Problem with SCR latching circuit
It is not guaranteed, but thyristors such as your SCR can act as GTO (gate turn off) devices.
Effectively the holding current increases if a low resistance is placed from gate to cathode. The connection diverts away some of the internal feedback current. Reverse bias on the gate can act similarly. If you make a synthetic SCR with two BJTs, it will always turn off with such a connection.
You will also observe a voltage from gate to cathode with the gate open and the SCR conducting current.
If you leave the switch connected to ground but add 1K in series with the gate you will see it behaving as you expected.