weird artifact with timeblend +timewarp on FLIP

[Memo]

I have a flip + whitewater sim which I've cached with all properties, now I'm slowing it down 4x (i.e. timewarp frames 1...6000 stretched to 1...24000) and I'm using timeblend (i.e. cache -> timeblend -> timewarp -> NULL_OUT)

 

Most of it is working, but for some reason there are some artifacts, some (very few) particles are not being interpolated. You can see what I mean in these videos (I'm rendering as seq of tiff with alpha and I've tried 3 diff alpha matting methods -ignore, straight, premult - and it's noticable on all).

 

https://www.dropbox.com/sh/wo2fm2qjd87vhbw/AACkLgoOCqFzehwz8pLyLEfGa?dl=0

(especially obvious when watched frame by frame). 

 

in the link above I've also included a tiny segment of my raw data and a minimal hip file which shows how I'm doing the timewarp+timeblend

 

I have no idea what this is, or even how to debug it. Any ideas welcome!

 

[Netvudu]

did you disable "reseeding" at the FLIP solver? Otherwise you have new particles appearing in the middle of the sim, and obviously those cannot be interpolated properly. 

[Memo]

Hi Netvudu, thanks for the reply. yes reseeding is disabled. Also the artifact doesn't look like a reseeding issue. It's not that I get 'occasional pops'. Instead, very small clumps of particles are not being interpolated. instead they are moving every 4 frames (you can see this in the videos - or directly in the hip). I can't figure out what it is about those clumps of particles that make them not interpolate. I've had a look at the geometry spreadsheet (or whatever it's called these days), and I can see my particles have a class attribute, and have values of 1 and 2. I've tried isolating class 1 and class 2, and both classes exhibit the same behaviour (i.e. tiny clumps in both classes of particles don't interpolate). I don't know how else to debug the problem. 

Edited December 1, 2015 by Memo