Accès mémoire invalide

<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 5.21.1

Error message:
Accès mémoire invalide.

Trace de la pile :
(00CF7737)
(00FD0EE2)
(00FD2F4A)
(00FCFD04)
(00097BBF) ntdll.dll
(00077B51) ntdll.dll.KiUserExceptionDispatcher
(00CF5BBE)
(00CF7F9E)
(00CF5983)
(00CF5A7B)
(00007515)
(00007B10)
(00007446)
(000B28BA)
(00021AF0)
(00280E1D)
(0027BF14)
(00280F83)
(00280E1D)
(0023B2E4)

(00FD154D)
(00FD2B27)
(00CF5B0A)
(00007515)
(00007B10)
(00007446)
(000B28BA)
(00021AF0)
(00280E1D)
(0027BF14)
(00280F83)
(00280E1D)
(0023B2E4)

Status: unknown_rel_addr

The problem happens rarely. I cannot reproduce it.