Drag and dropped a folder in the folder tree from one folder to another. The operation was successful, but this error message was thrown. WinSCP was connected to a Linux server through SFTP and port 22.

Windows 10 version 1607 OS build 14393.321
WinSCP 5.9.1

Error message:
Invalid access to memory.

Stack trace:
(008661A4)
(0008137F) ntdll.dll
(0006EF1A) ntdll.dll.KiUserExceptionDispatcher
(006C876A)
(006CD4D3)
(0040B1C3)
(00286808)
(0040BFF9)
(0028526F)
(0040C125)
(0024EA59)
(002859FE)
(0024EBBF)
(0024EA59)
(0024E0A0)
(00372990)
(0002C271) USER32.dll
(0000D845) USER32.dll
(0000D47B) USER32.dll
(00017AD7) USER32.dll
(0006EEF4) ntdll.dll.KiUserCallbackDispatcher
(0000FBCB) USER32.dll.SendMessageW
(000638A8) COMCTL32.DLL
(000200AF) COMCTL32.DLL
(0001F40C) COMCTL32.DLL
(0001DB01) COMCTL32.DLL
(00020B1A) COMCTL32.DLL
(0002C271) USER32.dll
(0000D845) USER32.dll
(0000CED2) USER32.dll.CallWindowProcW
(0024EB6A)
(00252ED3)
(00658CDE)
(0024EA59)
(002859FE)
(0024F493)
(00658CDE)
(0024EA59)
(002859FE)
(00372990)
(0002C271) USER32.dll
(0000D845) USER32.dll
(0000CED2) USER32.dll.CallWindowProcW
(0042BE5F)
(00372990)
(0002C271) USER32.dll
(0000D845) USER32.dll
(0000D47B) USER32.dll
(00017AD7) USER32.dll
(0006EEF4) ntdll.dll.KiUserCallbackDispatcher
(0000CF5B) USER32.dll.DispatchMessageW

Status: unknown_rel_addr

The problem happens rarely. I cannot reproduce it.