Thanks for the update, I appreciate it.
Right now when connecting the Play+ from its MIDI I/O TRS jacks to the OP-1 Field USB-C port, the Device page shows the USB Midi Interface as “Connected”, and MIDI flows. When connecting the Play+ from its USB-C port directly to the OP-1 Field USB-C port, the Device page says “Disconnected” for the same USB Midi Interface. Clearly, it can’t charge the Play+ and do MIDI at the same time correctly (or it’s a bug).
Thanks for the splitter reference – the reviews are a bit scary though. From what I read in the past few days, USB devices will first negotiate at low power how much they can charge each-other, then up the voltage from there; this implies a one-to-one conversation here, and it appears dangerous to change it to a one-to-two negotiation (OP-1 Field on one hand, and who knows what/who on both ends of that splitter).
Love the Play+, but I may consider a sequencer with an internal battery in the future. The OXY One seems to be popular but has no internal sound engines, and I do like the samples and synth of the Play+. The OP-Z seems the best fit since it’s in the TE family, but god knows what’s next with these guys, will there ever be an OP-Z2 or not? The Synthstrom Deluge checks a lot of boxes too: internal battery, internal samples/synths, a decent OLED screen, open-source firmware, faster internal storage, etc.
I don’t really blame the USB splitter manufacturers for not being able to provide what I need - these are mainly just simple accessories used for your single port phones. It’s kind of a miracle that I got a few of these working in the first place. 
But I do think it’s a shame that so many machines don’t have both a USB MIDI port and a dedicated power port, especially when they aren’t battery powered such as the Play or the Tracker. This means that they can never reliably do MIDI over USB except for when the other end also provides enough power.
It’s a good thing you’re considering different sequencers to accommodate a portable setup, I’ve always been intrigued by the Deluge. But I don’t think I’ll ever get used to any other workflow than the Tracker’s, so I’m stuck. 
Have noticed this same behavior when joining both OP-1F and ep-133 over USB C. When direct connected the ep-133 is listed as a connected device.
However when putting a USB hub in between them Retrkokits RK-006 it is no longer recognized as a connected device in the OP. But, the communication still works based on whatever you have setup. EP-133 still receiving clock and transport from OP-1.
Thanks. Just for reference for people stumbling upon this post. Here are two more tests that still didn’t work for me.
- Power bank in the top left.
- Belkin 4-IN-1 USB-C HUB below it, which supports pass-through power and can distribute some power to its 3 USB-C ports.
- Polyend Play+ to the left, which requires an external source of power via USB-C.
- OP-1F at the bottom.
My USB power bank (top left) is connected to the one USB-C port on the hub that is dedicated to receiving the power source (the leftmost port).
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in the left picture, the hub is connected to the Play and is passing-through power just fine it seems (since I can turn it on and hit “Play”). Once I attach the OP-1F to the hub with the gray TE cable, the MIDI device list is still empty, and no MIDI data is sent to the Play (no notes, no transport). I’m pretty sure the power is not even flowing from the OP-1F back to the hub (not that it would do anything), because I can see that icon on the MIDI page that says that the OP-1 is the one receiving power from the hub (I turned that icon on and off to test, no change).
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in the right picture, the hub is connected to the OP-1 directly (thus also powering it), and the gray cable is connected from the hub to the Play+ (thus also powering it; this hub can pass through power and distribute some to its other USB-C ports if I read its doc correctly). Still no MIDI device detected, no notes or transport sent.
Now if I connect the OP-1F to my new iPad mini directly (not pictured here), it shows up in AUM; no surprises here, the iPad is a nice USB host. If I connect the above Belkin hub to the iPad, then the OP-1F to the hub, same deal. Again, that’s the iPad being the USB host. Now of course what would be great is for me to be able to attach the Play+ to the hub too at this point, so that both OP-1F and Play+ are on the hub, the hub is connected to the iPad, and the iPad powers both machines (probably not for long). But that doesn’t work because the iPad cannot aggregate USB interfaces, so only one of those two devices will show up in AUM – unless somebody knows a trick (software trick, that is, I assume there is hardware that could do that in between, likely by iConnectvity, which would need to be powered too, adding more to this mess, etc).
So at this point I’m starting to suspect the OP-1F cannot act as a true USB host, and maybe is “just” a USB device (like the Play+) which has a few tricks up its sleeve to communicate nicely with other TE devices like the EP-133 or the OP-Z…
I think the hub itself not being powered might also be a factor here, which reminded me of one other option that I hadn’t tried until now.
When you connect a powered USB hub directly to the OP-1, it does extend its USB host capabilities onto the hub. The OP-1 won’t charge through the hub, which is unfortunate. But when I hook up the Tracker to one of the ports, it receives charge, and MIDI is being sent back and forth between the devices. The charge doesn’t come from the OP-1, because when I turn it off, the Tracker keeps going.
Since the OP-1 can hold a charge for a pretty long time, this feels like the second-best option. Admittedly, this is not a portable solution (unless you can find a battery powered hub), so it’s probably not what you’re looking for.
