If you move files using Dolphin and some of them overwrite others in the destination folder, the Panel and the Desktop will freeze temporarily.
The freeze duration is proportional to the number of files being overwritten, not to their size nor to the medium speed.

My platform is Manjaro (btw, maybe you could add it to the combobox).

Reproducible: Always

Steps to Reproduce:
In this example we'll build a test scenario:

1. Launch Dolphin and show the embedded terminal (press F4)

2. Run in the terminal the line below. This will create a folder 'test' inside '/tmp' and inside it a folder called 'subfolder'. It will also create in both folders a set of 50 empty files named '1' to '50'. I chose '/tmp' because in my system it is tmpfs, so we're working in RAM. Dolphin will end up showing the contents of '/tmp/test/subfolder'.

mkdir /tmp/test && cd /tmp/test && for a in {1..50}; do touch $a; done && mkdir subfolder && cd subfolder && for a in {1..50}; do touch $a; done

3. Select all files and press Ctrl-X to mark the 'cut'

4. Go up one folder to '/tmp/test' and press Ctrl-V to paste the files. When asked if you want to overwrite files, check 'Apply to all' and press 'Overwrite'

5. Quickly navigate to 'subfolder' to find it empty.

6. The Notifications icon on the Panel started showing the operation's progress but is now frozen as is the entire Panel and Desktop.

7. After a while all goes back to normal and you'll be notified the operation ended.