Thanks for your report.
I have sent you an email with a debug version of WinSCP to the address you have used to register on this forum.

<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 5.10

Error message:
Parent path not known

Stack trace:
(00899B75)
(0089B0A8)
(007ABCC6)
(006E064D)
(006DF146)
(006DE17E)
(006DC528)
(000A0BC7)
(00012368) kernel32.dll.BaseThreadInitThunk
(00038900) ntdll.dll
(000388D0) ntdll.dll

Status: unknown_rel_addr

I know how to reproduce the problem or the problem happens frequently enough. I wish to be contacted by the WinSCP team to help resolving the problem.