Here’s a couple things to check:
1. An earlier version of the Macchiato software sometimes showed this behavior. We believe your board has the latest software on it, but the only way to be sure is to download the latest from Github and re-flash it. (I see you just ordered a USB Tiny programmer.)
2. We had a generic USB-to-MIDI cable here in the Lab that proved to be a piece of junk. It was actually missing some components from its innards and yielded unreliable MIDI conversion, with all sorts of ill effects. This is not an uncommon problem. Here is an article on fixing a buggy cable.
3. The MIDI specification allows for two ways to tell a device to stop playing a note: with a Note Off message, and with a Note On / Velocity = 0 message. Theoretically they are equivalent, but we have seen several devices fail to respond reliably to one or the other. We developed the Macchiato to take Note On/Velocity 0 messages. Check your DAW. See which message it is sending. If there is an option, try to get it to send Note On Vel 0 in place of Note Off.