<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 5.7.5

Error message:
Out%20of%20memory%0D%0A%0D%0AStack%20trace%3A%0D%0A%28003B2122%29%20System%3A%3ANewUnicodeString%0D%0A%28003B2122%29%20System%3A%3ANewUnicodeString%0D%0A%280033F04B%29%20System%3A%3AClasses%3A%3ATComponent%3A%3AUpdateAction%0D%0A%28001DC01C%29%20Vcl%3A%3AForms%3A%3ATCustomForm%3A%3ACMActionUpdate%0D%0A%28002177B5%29%20Vcl%3A%3AControls%3A%3ATControl%3A%3AWndProc%0D%0A%280021C2F9%29%20Vcl%3A%3AControls%3A%3ATWinControl%3A%3AWndProc%0D%0A%28001D709C%29%20Vcl%3A%3AForms%3A%3ATCustomForm%3A%3AWndProc%0D%0A%280078C87D%29%20Vclcommon%3A%3AC2516_0%0D%0A%28002173F0%29%20Vcl%3A%3AControls%3A%3ATControl%3A%3APerform%0D%0A%28001E2253%29%20Vcl%3A%3AForms%3A%3ATApplication%3A%3ADispatchAction%0D%0A%280034021C%29%20System%3A%3AClasses%3A%3A_18201%0D%0A%28000152F7%29%20USER32.dll%0D%0A%2800015D35%29%20USER32.dll%0D%0A%2800015DE8%29%20USER32.dll%0D%0A%2800015E49%29%20USER32.dll%0D%0A%280000F117%29%20ntdll.dll.KiUserCallbackDispatcher%0D%0A%28000186D0%29%20USER32.dll.SendMessageW%0D%0A%28002125FC%29%20Vcl%3A%3AControls%3A%3ASendAppMessage%0D%0A%28001DBD1A%29%20Vcl%3A%3AForms%3A%3A_16777%0D%0A%28001DBD98%29%20Vcl%3A%3AForms%3A%3ATCustomForm%3A%3AUpdateActions

Status: not_matched

The problem happens rarely. I cannot reproduce it.