Jason, thanks for the speedy reply. I tested this 3.0beta firmware, and it's working great with the RK-08. However, the Octatrack and Digitakt are showing the problem with skipped/hanging notes.

This post solved my issue, but I wanted to add some more information. I took delivery of a brand new Poly Cinematic today and upon racking it and taking MIDI from my Elektron Octatrack, I immediately had issues with hung notes and skipped notes. This wasn't only from the Octatrack, but any notes that passed through the Octatrack. Not a great first impression. Further testing revealed: Elektron Digitakt has the same issue Retrokits RK-08 sequencer fails to trigger almost half of the notes, and hangs constantly. Plugging my Novation Midi Keyboard directly to the Poly Cinematic worked fine. I wasn't sure my factory fresh module was running 2.15, so I flashed it to be sure, and yes, same behavior. There is definitely something wrong with the firmware 2.15 and hardware sequencers, rolling back to 2.10 from this forum post, made it all work. Hoping I won't be stuck on this firmware forever, but glad the module is working as expected now.