ID 420326 - Exposure / clip warning doesn't work when using non nuke-default OCIO configs with use GPU for viewer enabled

Problem summary
Exposure warning doesn't work when using non nuke-default OCIO configs with use GPU for viewer enabled 

Customer reported version
nuke.12.0v3

Customer reported platform
centos7

Steps to reproduce

1) Open Nuke

2) Paste the below Checkerboard node into the node graph and view it

CheckerBoard2 { inputs 0 centerlinecolor {5 5 5 1} centerlinewidth 50 name CheckerBoard1 selected true xpos -18 ypos -262​}

3) Set clip_warning on the Viewer to exposure, the white cross will show the exposure warning

4) Open the Viewer properties, by pressing S over the Viewer, then enable use GPU for viewer when possible, the exposure warning will still work

5) Open the project settings, Edit>Project Settings.., and in the colour tab, set color management to OCIO, the exposure warning will still work

6) Set the OCIO config to aces_1.1, the exposure warning no longer works

Expected behaviour

For the exposure warning to work, as shown below:
​

Actual behaviour

The exposure warning no longer highlights clipped areas:

Reproduced by support
This bug has been reproduced in:

Nuke 12.0v3 - Windows 10 - CentOS 7.7 - MacOSX 10.13

Nuke 12.0v1 - Windows 10 - CentOS 7.7 - MacOSX 10.13 - regression

Unable to reproduce bug in:
Nuke 11.3v6 - Windows 10 - CentOS 7.7 - MacOSX 10.13

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