<Try to describe precise steps that lead to the problem (where do you click, what keys do you press, what do you see, etc.)>
<If relevant, consider attaching a session log file or a screenshot)>

WinSCP 5.6.3

Error message:
Invalid access to memory.

Stack trace:
[01205CFF]
[01806B82]
[01808BEA]
[01805B64]
[77B0389F] ntdll.dll

[013DFFEA]
[01806B82]
[01808BEA]
[01805B64]
[77B0389F] ntdll.dll
[77AF139A] ntdll.dll.KiUserExceptionDispatcher

[013DFC92]
[01806B82]
[01808BEA]
[01805B64]
[77B0389F] ntdll.dll
[77AF139A] ntdll.dll.KiUserExceptionDispatcher
[77B0389F] ntdll.dll
[01806B12]
[01808CFE]
[01805B64]
[77B0389F] ntdll.dll

[010CF74F]
[01806B82]
[01808BEA]
[01805B64]
[77B0389F] ntdll.dll
[77AF139A] ntdll.dll.KiUserExceptionDispatcher
[010D0DD0]
[010D1081]
[010B353E]
[0104B580]
[010A7BB9]
[0169E1E5]
[0169D8F0]
[01733800]
[0136F9BC]
[778D5B81] USER32.dll
[778B9D15] USER32.dll
[778B985B] USER32.dll
[778B96AB] USER32.dll.DispatchMessageW

[018071ED]
[018087C7]
[0169D07F]
[0169CEB1]
[010A600B]
[010A6482]
[010B35C2]
[0104B580]
[010A7BB9]
[01733800]
[0136F9BC]
[778D5B81] USER32.dll
[778B9D15] USER32.dll
[778B985B] USER32.dll
[778B96AB] USER32.dll.DispatchMessageW

Status: symbol_unknown

The problem happens rarely. I cannot reproduce it.