I know this is really high-level, but this is such weird behavior, and I can't figure out how to begin to fix this problem.
Every few minutes, Reaper will just pause in the middle of playback or recording. Not glitches or crackling... just nothing. No audio output, and the playback head doesn't move for a while. Obviously very frustrating while in the middle of tracking instruments, MIDI or audio.
Video of behavior:
https://youtu.be/Ll7fmSw5J6o
After capturing the video, I looked at my audio waveform and the 0.3 second pause looks close to 14,336 samples long. Which seems like 56 x 256 (buffer size)... which doesn't really tell me much, but maybe this is a clue? Either way it's frigging huge. My RME (UCX) Fireface USB Settings don't note any errors during playback, and LatencyMon isn't telling me anything useful.
Really looking forward to any help/ideas that you've got here...