I transfer NEF+JPG from a Nikon D80 to a local directory using Nikon Transfer. From Lightroom, I execute the Synchronize Folder... command using default settings (sync metadata is not selected). The sync process reaches approximately 74%, then hangs indefinitely. Task Manager shows no activity or significant memory usage. I must kill and restart the app to continue. Using Import Photos and Video exhibits the same behavior. Only reverting from 4.1 to 4.0 resolves the problem. The directory contains approximately 14000 photos, and I typically add 40 - 100 at a time. Never encountered an issue with 3.6.