What does the MIDI monitor show?  What's the routing topology?

Yamaha is going to be using realtime messages.  This is constant messaging even without any notes or controllers played.  I'm not sure how all of this is put together and I know the Erica can do filtering.  Not sure that's a good or bad thing (to filter) in your setup.  Not sure if that's turned on or not either.  

Thanks for your input. MIDI monitor correctly detects the first key/note pressed. All subsequent keys are marked as invalid messages. If you wait about 10 seconds, the first key/note is detected again, and so on. So far, I haven't defined any filters in MIDI Dispatch.

Yamaha's 'Active Sensing' messages could be a possible cause. If possible filter them out on your MIDI Dispatch device.

Thanks for your input. MIDI monitor correctly detects the first key/note pressed. All subsequent keys are marked as invalid messages. If you wait about 10 seconds, the first key/note is detected again, and so on. So far, I haven't defined any filters in MIDI Dispatch.

Yamaha instruments send 'Active Sensing' messages (0xFE) about every 300 milliseconds and there is no way to disable them. Some external devices don't deal with these properly and they give the appearance of a 'corrupted' midi stream.

One contributor to this is that some MIDI devices, including Yamahas, use 'Running Status' to save bandwidth by not re-sending the 'Note ON' status byte when multiple notes are played together quickly. 

Normally each 'Note ON' would use three bytes: a status byte, the MIDI note number and the velocity. But the midi spec allows multiple, sequential, 'Note ON' messages to omit the status byte and just send the note numbers and velocities. So sending 6 notes only requires 3 bytes for the first note and 2 bytes each for the other 5 notes: 13 bytes instead of 18.

Also a 'Note ON' with a velocity of 0 is interpreted as a 'Note OFF'. That allows even longer sets of note ON/OFF events to be chained together using just the one status byte at the beginning.

The problem arises when an 'Active Sensing' (0xFE) message gets sent in the middle of a string with no status bytes in the middle.

Not sure that is your problem but it sounds like it could be.

Thanks for your detailed post. I gave it a try. Unfortunately, it didn't work. My Ableton Push also sends Active Sense signals, but everything still works fine. I've borrowed a different MIDI interface (Kenton) and will give that a try.

Can you provide the text of the MIDI monitor info that shows invalid messages?  I'm hoping it shows the raw hex values along with labeling them as invalid to help analysis.

Please explain what 'I gave it a try.' means. What exactly did you 'try'?

Active Sensing messages aren't random but they might be occuring in the middle of a set of note on messages as described earlier.

Normally each 'Note ON' would use three bytes: a status byte, the MIDI note number and the velocity. But the midi spec allows multiple, sequential, 'Note ON' messages to omit the status byte and just send the note numbers and velocities. So sending 6 notes only requires 3 bytes for the first note and 2 bytes each for the other 5 notes: 13 bytes instead of 18.

Also a 'Note ON' with a velocity of 0 is interpreted as a 'Note OFF'. That allows even longer sets of note ON/OFF events to be chained together using just the one status byte at the beginning.

If an active sensing message is sent out after the initial status byte but before all of the rest of the 'chained' messages have finished the receiving device will get an 'invalid message' for any 'Note ON' event that is missing a status byte.

Just randomly trying things won't always produce the produce since it depends on the timing of the active sensing messages and you don't have any control over that.

You would need to create a long 'chain' of messages that only have one status byte at the start. But you don't have any control over that either.

That is why, as suggested, you need to capture a stream that includes the problem so it can be examined to see what messages are being sent.

In particular can you filter out the active sensing messages on the receiving device? If so does the problem go away when you do that?

Thanks for the tips. I’m happy to do all that and upload screenshots here. But guys, let’s be honest: why does it work with a
cheap Amazon interface and with other synthesizers too? But not with the Yamaha? That doesn’t make any sense. Why should I suddenly start messing around with MIDI filters now? I’ve never had to do that before.

Please try to understand that the ONLY info we have to go by in trying to help you is what you provide.

EVERYTHING that a yamaha synth does, or doesn't do, is because of the programming it is using. That programming includes global system settings as well as how a performance is configured.

Configuration includes:

1. the number and type (internal, external) of the parts

2. whether one or more arpeggios are being used

3. whether a motion sequence is being used

4. the channel configuration of the instrument and each part

In order to eliminate any of the above from being a possible cause we need to first know if you are using any of the above.

I can only get the first note to transmit.

Is that true even if you use an Init Normal (AWM2) performance?

Are you saying only one note EVER transmits for the performance you are using? You play one hundred notes one after the other but only the first one gets transmitted?

We are trying to understand the scope of your problem so we can try to reproduce it and/or narrow down what might be causing it. 

If necessary please create a user/library file of the performance, zip it up and post the zip file. Then we can load and examine the performance to see what the issue might be.

There's no reason to try to defend either Yamaha, other cheap stuff, or the Erica unit if your goal is to figure out what's going on.  I don't have any allegiance to any particular gear here.   Instead, I just ask for the stuff I think is going to help me make more sense out of what you're seeing.   It's fine not to want to work to figure it out or disagree on strategy.

Can't really answer anything about why one thing works and why another thing doesn't work without more info.  Not going to buy all the pieces to go solo on this either.

But, philosophically, I guess expensive stuff should work better than cheaper stuff but also more expensive stuff in this domain is usually more complex.  So there's that to deal with.  And Yamaha has a well earned reputation of choosing complexity and funky rules/exceptions just for the heck of it (most "simple" operations take a book to explain, not a pamphlet).  So that's something else to deal with.