I’ve noticed a problem at times when rendering my plugins in Reaper. I thought there was something wrong with my plugin latency reporting but it turns out to be an issue in Reaper.
When you select a “time selection” range in Reaper that time selection does not snap to nearest samples. You can actually select a time range that starts and ends in between samples. You can see this by zooming in on the time scale. When that rendered file is brought back in (with “Add rendered items to new track”) it’s timing is off by that amount - a fractional sample period - and it does not null with the source track.
I could not figure out how I was getting fractional latency - and that’s the reason. It seems to be a bug, or at least a design oversight, in Reaper and has probably been that way for a long time.
I don’t know if any other DAWs do this but so far I’ve only seen it happen in Reaper.