[Sync Source] in the [MIDI IN Settings] category in the Settings menu is set to other than [DIN MIDI] or [USB MIDI], but my Chordcat starts/stops by the MIDI signal start/stop message. Why?

This product can control the sequences by receiving MIDI signal start/stop messages from the MIDI IN input terminal or USB terminal regardless of the [Sync Source] setting value.
To disable the start/stop control of MIDI signals, go to the Settings menu >[MIDI IN Settings] category > [MIDI IN Start/Stop] and select [Disable].