ID 419010 - Switching visibility between Track Items is slower in Nuke 12 than Nuke 11

Problem summary

Switching visibility between Track Items is slower in Hiero 12 than Hiero 11.

In Hiero 12, the Viewer flashes to black, whereas Hiero 11 will switch visibility almost instantaneously.

Customer reported version
Hiero 12.0v3

Customer reported platform
CentOS 7

Steps to reproduce

1) Open Hiero and import the two attached clips.

2) Drag them onto the Timeline into separate tracks, with one directly over the other.

3) Disable the top track and notice that the Viewer goes to black before displaying the enabled track.

Expected behaviour
Track visibility should switch almost instantaneously, as it used to in Hiero 11.

Actual behaviour
Switching visibility causes the Viewer to go black before displaying the enabled track.

Workaround
Unknown.

Reproduced by support

This bug has been reproduced in:
Hiero 12.0v3 - Windows 10 - Linux CentOS 7 - macOS 10.13 (High Sierra)

Hiero 12.0v1 - Windows 10 - Linux CentOS 7 - macOS 10.13 (High Sierra) - Regression

Unable to reproduce bug in:
Hiero 11.3v6 - Windows 10 - Linux CentOS 7 - macOS 10.13 (High Sierra)

Earliest version tested
Hiero 11.3v6
- This issue doesn't appear in this version and has regressed