Hereby the offical answer from tc-electronic support.
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Dear Nicola,
Thank you for contacting TC Group Support.
Midi sync does not work properly on G-Natural. There is an offset. This is a known bug -
There is a workaround: use a MIDI CC to send the TAP tempo - from a MIDI track -
I.e. take MIDI CC# 15 and send
CC#15 = 127 on beat 1
CC#15= 0 on beat 2
CC#15 = 127 in beat 3
That should be enough to get the the tempo. This can be sent only at the start of the song or at any tempo change.
I hope this information has been helpful. If you should have any additional questions, please feel free to update this incident and I will be happy to assist you further.
Best regards,
Nicolas
Product Specialist
TC Group International