Invalid access to memory

<Try to describe precise steps that lead to the problem (where do you click, what keys do you press, what do you see, etc.)>
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WinSCP 5.9.1

Error message:
Invalid access to memory.

Stack trace:
(00011CB3) ntdll.dll.memcpy
(00052DD6) ntdll.dll
(0000F13E) ntdll.dll.KiUserExceptionDispatcher
(0001099E) kernel32.dll.WaitForMultipleObjectsEx
(000131FB) kernel32.dll.WaitForMultipleObjects
(000654E7)
(00063385)
(00016C61)
(0003CEDB)
(0003CE98)
(00372990)
(000152F7) USER32.dll
(00015D35) USER32.dll
(000167CE) USER32.dll
(00016895) USER32.dll.DispatchMessageW

Status: unknown_rel_addr

The problem happens rarely. I cannot reproduce it.