<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 5.9.3

Error message:
Error creating window device context

Stack trace:
(00251CF6)
(001F1D45)
(007DFA41)
(000C593B)
(000C61A8)
(000C637A)
(000C7E80)
(00099C12)
(0001CD5C)
(0008CEA1)
(00772A47)
(00775602)
(00775395)
(00787C38)
(0001EA8F)
(00045300)
(004169D3)
(00412728)
(0040847A)
(0042CA1F)
(00373100)
(0001B4B4) USER32.dll
(0001B5B2) USER32.dll
(0001BBE4) USER32.dll
(0001BC3B) USER32.dll.DispatchMessageW

Status: unknown_rel_addr

The problem happens rarely. I cannot reproduce it.