Problems with rotobrush 2: losing mask while freezing

Hello there,

I'm testing the rotobrush 2 on a relatively old machine (MBP 2013, AE 17.5.0) and I have the following issue.

I've applied rotobrush 2 to 4k footage and as long as rotobrush is propagating it's traking the subject I'm selecting pretty well, I can play the selection and it's quite precise BUT with that same selection when I'm freezing the effect the mask goes awry:

I've tried running rotobrush 2 at full resolution, with "best" quality, cleared the cache, relaunched AE...

Shortening the clip get rid of the issue for that particular frame but it looks more like a turnaround than a solution...

Matteo