Invalid access to memory

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<If relevant, consider attaching a session log file or a screenshot)>

WinSCP 6.1.2

Error message:
Invalid access to memory.

Stack trace:
(000C12D5)
(0009812F) ntdll.dll
(00077D31) ntdll.dll.KiUserExceptionDispatcher
(00024B84)
(00024E33)
(000BF6B7)
(00D21FD1)
(00D1E82D)
(0001BB4E)
(003CD663)
(0021564C)
(00031E01) USER32.dll
(00022BE1) USER32.dll
(000214A0) USER32.dll
(00020FEB) USER32.dll.DispatchMessageW

Status: unknown_rel_addr

The problem happens rarely. I cannot reproduce it.