Please check that you don't have a MIDI loop / echo occurring somewhere in your environment, where MIDI being received from the ARGON8 is being sent back to the ARGON8. It may be worth checking in MODALapp - click the Modal 'M' logo and navigate to 'Audio / MIDI Setup' > 'MIDI Forward' setting and uncheck this box.
Make sure you have the ARGON8 set to the same MIDI channel as that you are sending MIDI from, or enable the MIDI 'Omni' setting. However please note that if 'MPE Mode' is enabled then the selected 'MIDI channel' will only be applied to MIDI-out messages (and will not set what MIDI channel the synth will respond to) and the 'Omni' setting will be deactivated. Therefore if using any non-MPE MIDI sources when 'MPE Mode' is enabled, the non-MPE MIDI source channel must match the ARGON8 'MPE Master Channel' setting value of either 1 or 16, in order to function correctly. If you need to use a MIDI channel of 2-15, please disable the 'MPE Mode' setting.
Also please check the current MIDI filter settings.