Thanks for your report.

I've tried to upload a 4GB file to my hetzner box and it was super slow, then i got the message "Host is not communicating for 60 seconds" whereas the transfer was happily ticking behind it. Once I closed the message the transfer stalled and after a few minutes WinSCP was consuming over 2GB of RAM and this error popped up.

WinSCP 5.17.6

Error message:
Error reading ExplorerImages.PngImages: Error reading TPngImageCollectionItem.PngImage.Data: Out of memory

Stack trace:
(004FABD5)
(004FABD5)
(005003AC)
(0021E27A)
(0021E048)
(00395A3F)
(00394B3D)
(00395EF3)
(00395A26)
(00395279)
(0039525B)
(003A2ED5)
(003952ED)
(0039522C)
(003A2ED5)
(003900D2)
(00385B17)
(0038746B)
(003874F9)
(003A44DC)
(00E4D1AD)
(00E4D348)
(0002B1EE)
(00E41176)

(0039584B)
(00395A85)
(00394B3D)
(00395EF3)
(00395A26)
(00395279)
(0039525B)
(003A2ED5)
(003952ED)
(0039522C)
(003A2ED5)
(003900D2)
(00385B17)
(0038746B)
(003874F9)
(003A44DC)
(00E4D1AD)
(00E4D348)
(0002B1EE)
(00E41176)

(0039584B)
(00395A85)
(00395279)
(0039525B)
(003A2ED5)
(003952ED)
(0039522C)
(003A2ED5)
(003900D2)
(00385B17)
(0038746B)
(003874F9)
(003A44DC)
(00E4D1AD)
(00E4D348)
(0002B1EE)
(00E41176)

Status: unknown_rel_addr

I know how to reproduce the problem or the problem happens frequently enough. I wish to be contacted by the WinSCP team to help resolving the problem.