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 5.21.5

Error message:
Invalid access to memory.

Stack trace:
(00409ED8)
(00FDC86E)
(00FDE8D6)
(00FDB690)
(00097BBF) ntdll.dll
(00077B51) ntdll.dll.KiUserExceptionDispatcher
(00D0270B)
(00009B73)
(000166F3)
(00077C89)

(00FDCED9)
(00FDE4B3)
(00077CC9)

Status: unknown_rel_addr

The problem happens rarely. I cannot reproduce it.