Thanks for your report.

Moving our development server to a new IP address caused a URL -> IP translation anomaly for WinSCP. Ping, browsers and every other program opened content from the new IP address, while WinSCP acted strange, it connected to either the old or the new server. So I turned on logging, opened the log window, and tried to connect to the development server several times, then checked the log for IP. WinSCP always showed the same log, and it was not clear if it even logs the subsequent connecting attempts, or showing the first one. So while the log window was still open...

1. I went to Options --> Configuration --> Logging
2. Selected Display Complete Session (previously Display only last 200 was selected).
3. Clicked Ok.
4. In the still open log window tried to click the Clear Log button.

That's when the error message appeared. Please feel free to contact me for further details, if necessary.

WinSCP 5.7

Error message:
Error occurred during logging. It's been turned off.

List index out of bounds (0)

Stack trace:
[013235F5]
[013235F5]
[0160FDB2] @TLogMemo@WMLogUpdate$qr24Winapi@Messages@TMessage
[01610A76] @TLogMemo@Dispatch$qqrpv
[0121C755]
[0121BD9C]
[01340678]
[774662F7] USER32.dll
[77466D35] USER32.dll
[774677BF] USER32.dll
[77467885] USER32.dll.DispatchMessageW

[013235F5]
[013235F5]
[0160F635] @TLogMemo@SessionLogChange$qqrp14System@TObject
[016C8185]
[0170C2A4]
[01340678]
[774662F7] USER32.dll
[77466D35] USER32.dll
[774677BF] USER32.dll
[77467885] USER32.dll.DispatchMessageW