MIDI doesn't care about what device is sending or receiving a message; it only cares about channel number. It sounds like both App X & Y are listening on the same channel, for example Channel 1, and both Keyboard 1 & 2 are transmitting on that same channel.

Thanks Lex. That's true because this is concerning to MIDI communication. However MD/BT01 are HW devices and they communicate to the iPadPro via Bluetooth.
MIDI is over the Bluetooth communication. Why should I impose a different channel ?

I suppose the MD/BT01 should first "pair" with the controller (iPadPro) - as any other bluetooth device does - then the communication between the devices and the iPadPro may take place ( in this case the MIDI communication ). For example think to a bluetooth earphone.

With the MD/BT01 the devices automatically pair to the iPadPro when power is up and they connect to iPadPro.
But I'm pretty sure they use an identical "name" (maybe it is burned in the HW) so it is not possible to address and to set up two separate communication channels.
They are two devices but since the communication has the same "name" the MIDI communication goes exactly to both devices because they are the same !

This is a bad limit. That mean that I can use ONLY ONE device at time, unless I force, at MIDI level, the channel assignment: a very very poor limitation.

I thought to solve the cable problem. It is not. I just introduced an additional problem (and a little bluetooth latency problem).

Do you know anyone in Yamaha who can fix the problem and explain the trick above ?
In my view Yamaha should clarify this in the web store to avoid that people unknowingly buy more than one devices in the hope to solve a MIDI "cable problem".

Maybe try AUM matrix.

https://forum.audiob.us/discussion/26784/yamaha-md-bt-01-two-keyboards-one-ipad

Use of multiple devices is implied as supported here: https://www.yamahasynth.com/yamaha-synth-rss/bluetooth-wireless-midi-adaptors

There's likely a way to do this without having to have one set of MIDI channels on one device and another set on the other device.

What are you connecting the MD-BT01 to? As in ... PC/Windows, Mac/MacOS, iPad/iOS, Tablet/Android, etc?

The app in the referenced thread I believe is for iOS - but you may not be using that environment.

Hi Jason, I only use IOS 13 iPadPro.
tried AUM (great app), however I didn't solve. I also had a look at the first suggested link, however I cannot trust someone connected 8 devices with MD/BT01.
However I did a little step forward.
I launched Module app from Korg and Sound Canvas app from Roland. On the Setting of any of them you can "connect" to the two MDBT01 device that I have inserted in the two keyboards.
However I noticed that ONLY Sound CANVAS allows to check on which of two MDBT01 to let the MIDI flow.
Module app has not this option.
I installed Yamaha Synth Book app, and this also has the option to select to what MDBT01 to let MIDI flow.
I also started AUM, however only SoundCanvas and Yamaha Synth Book can separately be played by the two keyboard. I'm still working on it.
I'm convinced that almost all software are not being designed to work with Bluetooth devices natively.
It is a strong limitation that do not let use MDBT01 properly.
We are long away from performing wireless.
Only AUM or AudioBus may overcome such limit trying to directly manage Bluetooth connections by means of a Virtual Bluetooth capability.
It is a lost game. ?

I do not have as much experience with iOS as other environments. I know Android Bluetooth MIDI is relatively new and not well supported. iOS I would expect a better experience although I do not have a second Bluetooth MIDI device to try this out.

Hopefully someone can help.

I've a question to Yamaha people: why do not let MD-BT01 be discoverable to IOS and thus directly usable by MIDI devices via any MIDI Software? This will make MD-BT01 pervasive. Today it is just a toy for children. I really appreciate an answer, at least because they created a lot of expectations ( device latency is really low ) trying to solve the MIDI cable problem.

Sorry, I don’t understand what you are asking. As you know, since you are running SynthBook on an iOS device.
What “cable problem” are you referring to?

I hope you are a Yamaha representative who knows the device.
Maybe you didn’t read previous comments. Please read from beginning. It takes 2 minutes.
The subject is MDBT01 and it is supposed to be an alternative to a “MIDI cable”. Isn’t it ?
A Bluetooth wireless MIDI communication in alternative to a MIDI cable. This what Yamaha states. Do you agree ?
If yes, have you tried to use nr. 2 MDBT01 device in the same environment? Please read my very first note.
They cannot be separately addressed. That’s a strong limitation.
Again: why Yamaha do not let MDBT01 be discoverable to iOS Bluetooth so that any SW MIDI can discover each and connect/communicate via MIDI separately ?