After running an HDR stack and enabling Denoise, Lightroom displays ‘Downloading original…’ but the progress bar never moves. Task Manager shows zero network activity from Lightroom or Adobe, so it looks like a backend fault.
[moving from bugs to discussions according to the comunity rules - Mod.]
Could you please share the version of Lightroom you're currently using? You can find it by going to Help > System Info, then copying and pasting it into a text file to attach here. What type of file are you trying to denoise, and has this happened before? This will enable us to investigate it further.