ID 466250 - Tracker node unable to start tracking until postage stamped Shuffle nodes have finished loading

Problem summary
It is common practice to enable the postage stamp option within the a Shuffle node when splitting out passes from a multichannel exr file, as it greatly assists with seeing a visual representation of the pass in the Node Graph.

With larger multichannel exr files this process of generating the postage stamped Shuffle nodes can take a bit of processing time within Nuke. It has been discovered that if during this loading time, you attempt to track another Read node in the script, it is not possible to track until the postage stamps are loaded.

Note: This only occurs on the first time the Shuffle nodes are created or accessed in the session, as once cached they are loaded quicker.

Customer reported version
nuke.11.3v5

Customer reported platform
ubuntu

Steps to reproduce

(follow steps in attached script)

or

1) Read in an multi-channel exr file that has a significant amount of layer (15+)

2) Read in a separate image sequence to be used for the tracking

3) Add in a Tracker node, and set up ready to track an area of the image sequence.

4) With the multi-channel exr Read node selected, run the following code in the Script Editor (to split all the channels and automatically generate as postage stamps)

​​​nodes = nuke.selectedNodes()
for node in nodes:
    if node.Class() == 'Read':
        channels = node.channels()
        layers = list( set([channel.split('.')[0] for channel in channels]) )
        layers.sort()
        if 'rgba' in layers:
            layers.remove('rgba')
        for layer in layers:
            shuffleNode = nuke.nodes.Shuffle(label=layer,inputs=[node])
            shuffleNode['in'].setValue( layer )
            shuffleNode['postage_stamp'].setValue(True)
    else:
        pass

5) As the postage stamped Shuffle nodes are loading, start the track on the image sequence.
Result: Track will not initiate, until the Shuffle nodes have finished loading.

Expected behaviour
It should be possible to track another Read node, when the postage stamped Shuffle nodes are loading

Actual behaviour
The postage stamped Shuffle nodes are taking priority over the tracking request.

Workaround
Disabling the postage stamps will avoid this issue, or waiting till the postage stamps are generated before tracking is an option.

Reproduced by support
Guidance: Have you reproduced the problem? In which versions have you reproduced the problem? DELETE THIS LINE

This bug has been reproduced in:
Nuke 12.2v4 - Windows 10 - CentOS 7 - MacOS 10.15.6
Nuke 12.2v1 - Windows 10
Nuke 12.1v1 - Windows 10
Nuke 12.0v1 - Windows 10
Nuke 11.3v1 - Windows 10
Nuke 11.2v1 - Windows 10
Nuke 11.1v1 - Windows 10
Nuke 11.0v1 - Windows 10
Nuke 10.5v1 - Windows 10
Nuke 10.0v1 - Windows 10
Nuke 9.0v1 - Windows 10 - CentOS 7 - MacOS

Earliest version tested
Nuke 9.0v1
- This issue appears to be in all versions of the product