FTP - Viewer Pane for image files is slow

[TrialUserSoFar]

Because Thumbnails mode in FTP locations is disabled, means you are not supposed to fetch previews for files there.
While you still can enable Viewer Pane. When it's enabled, image files are loaded after a 70 seconds delay. 700KB, 500KB all had similar delay.
Sometimes smaller ones are loaded quickly. (120KB ones are quick, and 150KB are slow)

Here is seems same problem reported many many years ago. But without any response.

Viewer pane freeze in FTP with jpg (v 10.5.7.0)

Quite often with FTP while looking through a list of jpg images, Opus will freeze with the viewer pane saying "loading...". Even when files are <1mb. It will usually hang for several minutes but sometimes it goes to a white screen and I have to kill …

227 PASV Passive mode (192,168,0,173,141,109)
150 RETR sending file
425984 bytes received in 0.27 seconds (15407.232 Kbytes/sec)
226 RETR Done
227 PASV Passive mode (192,168,0,173,133,39)
150 RETR sending file
226 RETR Done
** CloseFile NO FD_CLOSE Response from Server **
21802 bytes received in 70.953 seconds (0.0 Kbytes/sec)
227 PASV Passive mode (192,168,0,173,137,251)
150 RETR sending file
226 RETR Done
800773 bytes received in 0.93 seconds (8408.208 Kbytes/sec)
227 PASV Passive mode (192,168,0,173,174,239)
150 RETR sending file
226 RETR Done
** CloseFile NO FD_CLOSE Response from Server **
23131 bytes received in 70.625 seconds (0.0 Kbytes/sec)

[Leo]

** CloseFile NO FD_CLOSE Response from Server ** usually means the other end didn't close the data connection properly, which causes a long delay waiting for the closure to happen.