The following happens only when Stylus RMX is loaded in SX3: if there is a lot of MIDI traffic generated by a controller (MACKIE control select/mute/solo button pressed) all MIDI traffic stalls for about 5 seconds. Sometimes it happens too when the sliders are moved, but not often. These don't have to be Mackie sliders, but can be of a different controller (KORG microKONTROL). All MIDI devices are on separate MIDI interfaces. No MIDI Thru is used. The MIDI interface is on a USB bus, like the microKONTROL.
Has anyone any idea(s) what it can be?