ID 239243 - Viewer with onionskin enabled does not update reliably

Problem summary
Onion Skin does not reliably update in the Viewer.

Customer reported version
Nuke 11.3v4 

Steps to reproduce

1) Open Nuke.

2) Read in an image sequence (an example is attached).

3) Create a Rotopaint downstream of the footage.

4) On the RotoPaint, choose the Clone tool, set an offset, paint a clone stroke.

5) Check the Onion option in the Viewer.

6) Set the stroke's life to "all".

7) Move to frame 2 and notice that the Onion Skin will update:

8) Move to frame 3 and notice that the Onion Skin stops updating:

Expected behaviour
The Onion Skin should update every frame to show the Paint source overlayed in the Viewer.

Actual behaviour
The Onion Skin doesn't update reliably.

Workaround
Unknown. 

Reproduced by support

This bug has been reproduced in:
Nuke 12.1v1 - Windows 10 - macOS 10.13 (High Sierra) - Linux CentOS 7

Nuke 12.0v1 - Windows 10

Nuke 11.0v1 - Windows 10

Nuke 10.0v1 - Windows 10

Nuke 9.0v1 - Windows 10

Nuke 8.0v1 - Windows 10 - macOS 10.13 (High Sierra)

Earliest version tested
Nuke 8.0v1
- This issue appears to be in all versions of the product