Electric bass phantom notes

I’m very, very confused and would appreciate some help.

I have music in Sibelius Ultimate which includes a bass part. With Halion activated within the notation software, I can hear the bass part played with the Init Electric Bass samples. All good. However, a couple of notes sound with a second one added that is not present in the score. It’s all rather bizarre. At first I thought my Arturia KeyLab 88 MkII might be failing and causing a problem, but the phantom notes persist; the note C (written Middle C) sounds with an A flat beneath, for example. I have created a new score and still the problem persists. I am at a loss to understand what might be causing this problem. Any and all help will be greatly appreciated.

This is all I can think of: Have you turned off Ghost Notes in the Electric Bass’s settings?
[https://steinberg.help/electric_bass/v1/en/_shared_picts/picts/halion_instruments/electric_bass/electric_bass_settings.png](Electric Bass Settings image)
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Settings Pane

Huge thanks for responding, and so quickly! Much appreciated. I am a little perplexed by this setting and will need to have a read of the manual - apologies, I should have done this in the first instance!