Hello julien

> but it wasn't a problem before the upgrade and all my other synths are
> plugged the same way with no issues???

yes. Because the JX3P did not send and receive controller data before
the upgrade.

Simply try to switch off the MIDI thru function at the sequencer.

In a forthcoming version of the JX3P-Firmware, there will may be a
setting function for the keyboard, which will avoid that.