Invalid access to memory

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WinSCP 5.21.1

Error message:
Invalid access to memory.

Stack trace:
(003AB46D)
(00097FCF) ntdll.dll
(000761E1) ntdll.dll.KiUserExceptionDispatcher
(0023F6B9)
(00280E1D)
(0023B2E4)

Status: unknown_rel_addr

The problem happens rarely. I cannot reproduce it.