Nuke can frequently become unresponsive for a few seconds or be slow to work with when Tracker nodes are present in a script. This happens specifically when the Tracker nodes are generating preview patches of keyframes. Keyframe preview task messages can also appear when performing other tasks like rendering, and cause a significant slow down.
The preview patches for the tracking keyframes that appear at the top of the Viewer window during tracking, are pulled in from the upstream node tree so the patches will have all operations happening above the Tracker node applied.
If you have a lot of keyframes, or CPU expensive operations above the Tracker node, it can take a long time to rebuild the patches for preview.
If you are experiencing slowdown with a similar setup then please try turning off the keyframe previews during tracking.
You can turn off the keyframe previews in the Settings tab of the Tracker node by setting
General > "show zoom window" to "never"
Keyframe Tracking > "keyframe display" to "none" (highlighted below in red).
When you are doing hand-tracking, you can disable keyframe patch creation by turning off "create new key when track is moved" (highlighted below in yellow).
If this doesn’t stop Nuke from becoming unresponsive, the UI freezes might be related to the autosave functionality in Nuke. For more information, please see this article: Q100199: Slow performance/UI freezes when working with scripts that contain Tracker nodes
For more information on how to open a Support ticket, please refer to the 'Using the Support Portal' article.