I have a 12 minute movie that I converted to jpgs. So I have in a folder 17620 jpgs of 1920x800 pixels each.
I wanted to move them to another folder so I selected a few of them in Nemo and it just hangs: a popup window appears saying it is going to move the files but it hangs. You end killing nemo and look if he moved or not the files. Yes, it moved the files, only it hanged in the process (I was looking to the cpu use and kill nemo when the cpu use was again near 0%).
I tried then with around 400 files only. All my tries Nemo hanged.
I deactivated the preview of images and also the counting of files in folders, my guess was it was doing the previews or counting. But no way. it continues to hang when heavy number of files to copy or move is the job.
So I was to Software Manager, searched for "file managers" and the best rated was "gnome-commander". I downloaded it and it remembered me of first years using Linux, probably it was this program. Ugly interface but... holy sh*t, does the work! I moved my 17 thousand files without any problem.
So: Nemo has a serious problem with heavy jobs.