<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 5.7.7

Error message:
Invalid%20access%20to%20memory.%0D%0A%0D%0AStack%20trace%3A%0D%0A%280060C139%29%20C2280_0%0D%0A%28007E08AA%29%20C4799_0%0D%0A%28007E2912%29%20____ExceptionHandler%0D%0A%28007DF88C%29%20__ExceptionHandler%0D%0A%2800081D3F%29%20ntdll.dll%0D%0A%280006F8EA%29%20ntdll.dll.KiUserExceptionDispatcher%0D%0A%2800609AC2%29%20_count234%0D%0A%2800609FC7%29%20_add234%0D%0A%280060DB20%29%20_sk_newlistener%0D%0A%280060DB45%29%20_sk_newlistener%0D%0A%28005E34C3%29%20_new_listener%0D%0A%28005E2963%29%20_pfd_addforward%0D%0A%28005EB49A%29%20_sshfwd_unthrottle%0D%0A%28005F349A%29%20_sshfwd_unthrottle%0D%0A%28005F0673%29%20_sshfwd_unthrottle%0D%0A%28005F3CB3%29%20_sshfwd_unthrottle%0D%0A%28005E80CA%29%20C2232_0%0D%0A%28005E8274%29%20C2232_0%0D%0A%28005E8534%29%20C2232_0%0D%0A%280060E031%29%20_select_result%0D%0A%28006A9A83%29%20TSecureShell%3A%3AHandleNetworkEvents%0D%0A%28006A9D46%29%20TSecureShell%3A%3AProcessNetworkEvents%0D%0A%28006A9337%29%20TSecureShell%3A%3AWaitForData%0D%0A%28006A46F1%29%20TSecureShell%3A%3AInit%0D%0A%28006A4019%29%20TSecureShell%3A%3AOpen%0D%0A%280070E3C0%29%20TTerminal%3A%3AOpenTunnel%0D%0A%280070CDAA%29%20TTerminal%3A%3AOpen%0D%0A%280067224C%29%20TTerminalItem%3A%3AProcessEvent%0D%0A%2800670728%29%20TSignalThread%3A%3AExecute%0D%0A%280008269F%29%20Userinterface%3A%3AC21_0%0D%0A%28000152C2%29%20KERNEL32.DLL.BaseThreadInitThunk%0D%0A%280005FFD7%29%20ntdll.dll%0D%0A%280005FF9F%29%20ntdll.dll%0D%0AAuthentication%20log%20%28see%20session%20log%20for%20details%29%3A%0D%0AUsing%20username%20%22jbathman%22.%0D%0AAuthenticating%20with%20public%20key%20%22imported-openssh-key%22.%0D%0A%0D%0AAuthentication%20failed.

Status: not_matched

The problem happens rarely. I cannot reproduce it.