I did not reproduce this. You did not follow the instructions in the bug post template. Your steps are vague and confusing because it does not use Shotcut’s terminology (the names of things in the user interface). For example, what exactly does “pull in a video into preview” mean? At what step does the proxy generation job start or was it already generated previous to these steps? Is it possible the problem you experienced unrelated to these steps and more due to something else such as the structure of the source media file?