I can't start/stop the SQUID from the connected external device.

Two main factors can cause this and there are two possible countermeasures.

1. If the [Start/Stop] in the [MIDI IN] setting category of the GLOBAL menu is set to [Disable], the start/stop signals from the external MIDI devices will be disabled. Please set it to [Receive].

2. If you are connecting a mono mini jack cable to the CLOCK IN terminal, start/stop signals from the external device can't be received. please use a stereo mini jack cable.
Also, if you want to trigger sequences of this unit with audio signals, you'll use a mono mini jack cable. In that case, please use the play/stop button of this unit or input the start/stop signals from the external MIDI device.