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

WinSCP 6.1.2

Error message:
Invalid access to memory.

Stack trace:
(0034407F)
(0003EC2E) ntdll.dll.ZwWow64CallFunction64
(0003F3AA) ntdll.dll.KiUserExceptionDispatcher
(00514A2B)
(00E6E5A3)
(00E6DBA4)
(00E71A2E)
(00263504)
(003470CE)
(003B5D1E)
(003B5D1E)
(003B5D9C)

Status: unknown_rel_addr

The problem happens rarely. I cannot reproduce it.