John,
Bit of confusion there sorry. Forgot you were using a different HV board but the same applies anyhow.

Saying the SCR is not turning off I'm assuming you mean it is running at exceptionally high frequency.

SCR can only turn on once because of cap in the gate lead and then off again when it dumps the HV into the coil.

If running at high hz then yes, getting a high hz signal.

You did say it is only when magnet is over the hall switch, is this still the case, then and only then...??