Out of system resources

<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 5.9.2

Error message:
Out of system resources

Stack trace:
(001F1A37)
(001F1ADA)
(001F1B0B)
(001F6D07)
(001F8DC3)

Status: unknown_rel_addr

The problem happens rarely. I cannot reproduce it.