Now I can say that I ran into a problem. I was working on a project from a video, editing the audio to add back to the video track and everything suddenly started getting distorted, it got noisy and then Reaper went wonky. Meters were bouncing randomly, and I couldn't stop playback. I closed Reaper, restarted and got to the point that I could render the file, and got the video done. I thought maybe it had something to do with using the video file and moved on.
Yesterday, I was working on a recording with just 4 tracks, only 3 or 4 minutes long. It had an MT POwerdrumkit track, and a guitar, bass, and vocal track. Only a couple of plugins (stock ReaEQ and Comp) and a reverb and zero track edits. Everything was simple. Suddenly things got distorted on playback, meters bounced and I was stuck.
I tried resetting the Tascam interface, as it seemed it might be an ASIO issue, since Windows audio seemed to work just fine. I've deleted and reinstalled the V4.0 drivers, and have been able to work the file, did a bit of editing and haven't had an issue since.
Hopefully things will continue to work. I'm still running Reaper 5.99, since my license was for versions 4 & 5 so I know it's not a due to a Reaper update.