MP201 MIDI Through Problem

[kenficara]

I have been using an iPad and camera connection kit as a MIDI controller for a number of effects units including a Strymon Timeline. If I connect the iPad to the Timeline directly, it works flawlessly; CC messages change values smoothly with the motion of the controllers. However if I pass it through the MP201 (iPad plugged into MP201 MIDI in, cable from MP201 out to Timeline In), the Timeline sometimes doesn't respond at all or only gets some of the messages. The values jump around or don't change as I change the controller.

I have checked all the obvious:

iPad is sending on Channel 3 which is what Timeline receives
MIDI merge DIN is set to DIN out
I have lowered the MIDI governor setting all the way to 0 with no apparent change

Any thoughts? It's particularly important because the Timeline uses CC messages in restricted ranges (0-11, 0-18) and there's no way for the MP201 to send like that.

thanks
ken