Why am I getting a white line when rending object separately

[Whispermode]

No need for that, thanks!

It's a general problem and we've just fixed it.

@Lino - is this release on the way yet?

[linograndiotoy]

It's available now.

[Whispermode]

It's available now.

Just downloaded - I now have a black line around the object in viewport but the render (F12) looks good. Can't figure out the discrepancy...

EDIT: to clarify - I'm on 'Override' for the Imager and Postprocess. If I uncheck Override, the image gets darker, but the outline remains, which must mean it's outside of the Imager(?) 'Disable partial alpha' makes the whole background black.

Again, the F12 view looks great.

EDIT 2: There's definitely a problem between how viewport and F12 manage shadow catchers and the post processor. I'm on a deadline, but will see if I can recreate later.

[pegot]

I sometimes have this issue too – usually when working with cryptomattes.

Since your files are .exr, one thing you can try that sometimes helps is to apply the EXtractoR effect in After Effects. This is really supposed to be used with multi-layer .exr files but I found it can sometimes create a tighter mask around a single alpha render. The effect also contains an UnMult checkbox.