Unstable sync between mod duo and mod dwarf

The mod dwarf seems to be the problem, I can record loops from the duo onto the Boss RC-500 with no problems, but the mod dwarf is always out of sync, so missess the primary beat in the recording. Also, the mod dwarf tempo is swinging between 144.00 and 144.35. It’s really uncomfortable as within a minute or so they are out of sync and it doesn’t seem to make sense. Can anyone help?