ZED-6: Synth only works with Hi-Z

ZED-6: Synth only works with Hi-Z

I’m wondering if this behavior is normal or if there might be something wrong with my Allen & Heath ZED-6.
My Novation Bass Station II is connected to one of the mono channels using a standard 6.3 mm TS cable into the line input. However, I only get a proper signal when I engage the Hi-Z/Instrument switch. With the switch turned off, the signal is extremely weak or practically inaudible.
As far as I know, the Bass Station II outputs a line-level signal, so it should work with the line input without the Hi-Z/Instrument switch enabled.
I have tested both mono channels and they behave the same way.
Is this normal for the ZED-6, or could there be a fault with the mixer? Has anyone experienced the same issue?

Thanks in advance!