Some insight, as I try and figure this out.
1: This is tied only to Team Render, even if it's on the same machine.
2: It's tied to Physical Render, as Standard works fine.
3: It's connected to High Q, I think. I unchecked it at some point and it rendered ok, but then it inexplicably stopped rendering ok. I'm not sure what I did, but I can't get it back.
4: It's only with xpCache, again even on the same machine. If I render with team render NO cache... it's fine.
: Oddly, I have another file that uses xpTrail, I use a sweep nurb, uses xpCache w/ external files, and it's rendering fine. But I cannot re-create even the most basic file and have it work, so not sure how that file is different other than I created it in R19 last year.
My feeling is that somehow the xpCache is getting read or written incorrectly based on something Physical Render is looking for. So, no matter what the range of frames (say 50-60), it isn't finding the cache file the first frame, even though it's loaded correctly (as indicated in the console log).
I'm including this basic file with no bells or whistles, just a basic emitter, sweep nurb, and xpCache. You'll have to build/use an xpCache to see that it wont render frame 50, even though the geometry is well established.Test-Basic-Sweep.c4d