If you browse a SSHFS folder[1], for example /tmp/folder in this case, and go into a crowded subfolder like /tmp/folder/foo, Dolphin will slow down a lot the user interface, till being totally unresponsive for some seconds:
- when in detailed view, I noticed that Dolphin takes seems to be working on populating the "size" column, with the number of elements in each subfolder of /tmp/folder/foo
I assume it is working on size column because I can see Dolphin populating the size entry one by one;
- when in compact view I open a folder, Dolphin seems to be working on detecting what is the type of the files, because as soon I get inside I see the files with a "?" (question mark) icon, then Dolphin assigns the correct icon. For example if a file is a text, assign a text icon, etc.
Note:
- I disabled thumbnail preview in Dolphin;
- I am experiencing this problem also when running in a LAN, so it cannot be a bandwidth problem;
- Dolphin CPU usage seems to not grow when the slowness quirk is happening

[1]:
mounted for example with command
sshfs -o cache=yes -o kernel_cache -o compression=no user@192.168.1.40:/zpool_1/foo /tmp/folder
or with a more simpler command
sshfs user@192.168.1.40:/zpool_1/foo /tmp/folder