sync/jitter problems using Motu MicroLite

[chemie]

Hello guys,
I'm facing huge problems with MIDI sync of my MicroLite. This is my setup:
Live masterclock, sending sync via MIDI to:
a) Elektron, which has its own sequencer
b) xoxbox, which has its own sequencer

everything is more or less in sync (variation +/- 0.1 bpm), until I do not decide to play a MIDI clip: as soon as MIDI messages are sent to any other instrument (the MCV4 in this case, but I also tried sending MIDI notes to others), MIDI sync oscillates +/- 20-30 bpm!

I've tested a Prodipe 4i4o instead of Motu MicroLite and...it works with the same setup!
I've tested my Motu MicroLite in another studio and...it works!
Am I missing any configuration?

Operating System: Mac OS 10.10 (Yosemite)
DAW: Live 8 (32-bit) (version: 8.3.4)
Hardware: soundcard: Motu Ultralite mk3 Hybrid
MIDI interface: Motu Micro Lite
drum machine: Elektron Machinedrum SPS-1 mk2
MIDI to cv converter: Doepfer MCV4