Happy new year, @Takumi_Ogata!
Unfortunately I spoke too soon… it’s still easy to get things to break even in version 5.4.0, all I have to do is use 5-6 fingers on my Linnstrument, which apparently produces more MIDI messages than the current UART implementation is able to handle.
I’ll try it over USB, too, to see if that makes the problem go away. But even if that is the case, it would be nice to fix this issue.
Best,
Alex
Happy new year, Alex!
Thank you for keeping us posted about the experience. Could you tell us more about the code that you flashed?
This weekend I experimented a little bit more, and I discovered that the problem was not w/ the Daisy library but rather with the code that I wrote in the audio callback. Sometimes it would do too much work (i.e., it wouldn’t return in amount of time allotted) which resulted in a nasty crash. When I commented out that code, the Daisy correctly received all of the MIDI events from my Linnstrument no matter how many fingers I used.
I solved the problem by making my code a little more efficient and limiting the number of voices. So I’m back on track 
Sorry for the confusion!
Thank you for the update and I’m glad to hear that it’s working!!