Comment 1 for bug 2018248

Yes, I've had the autoadd folder stall when there's big files in there. Would not suggest using the Downloads folder for this reason - set to a subfolder and move the files you want in there.

A couple of things:
1. The Job Spy plugin has an option buried in its menus to "Tickle the Auto-Adder." This sometimes helps.

2. Input plugins occasionally interfere. Right-click preferences button and restart with plugins ignored to see if this is the case. Note that this will turn off things like DeDRM (which runs on import).

3. Even then, large files you may just need to add manually.