Just another sync problem - PO-20 and microbrute

Please help!

I already looked at the really comprehensive youtube-videos explaining how to sync the microbrute to the pocket operators, but I´m still having problems.
The MB is master with a cable running from its gate out into my PO-20´s input. The PO is on SYN2.
If I press one key on the MB the PO detects it and plays exactly one step. But as soons as I start the MB´s sequencer, there is also just one step from the PO and no further steps.
I know that I cannot put rests into the MB´s sequence and that the rate shouldn´t be too high.
Apparently the PO detects the input on the MB if I repeatedly press a key but that way both devices aren´t really playable.
Could this be an issue of the PO-20 (I do not yet have any other PO´s)?

Any help is very much appreciated!