I tried running the command "c:\Program Files (x86)\WinSCP\WinSCP.com ... etc." directly from the Command Prompt and got the same result, i.e., WinSCP seems to start and immediately displays that list of settings on the console instead of outputting them to the specified log file, then displays "Host:" and waits for a response.
I then tried running the batch file in Windows PowerShell and got the same result.
Lastly, I ran the command directly from the command line in PowerShell and got a different result, an error message telling me that I "must provide a value expression on the right-hand side of the '/' operator" referring to the "/ini=nul" clause. I tried running it again without that clause and got the same error, this time referring to the "/log=" clause.
This monthly process ran successfully last month. Here are a couple of lines from the log of that run showing the version:
. 2018-11-19 14:57:12.000 WinSCP Version 5.9.5 (Build 7441) (OS 6.1.7601 Service Pack 1 - Windows Server 2008 R2 Enterprise)
. 2018-11-19 14:57:12.001 Configuration: HKCU\Software\Martin Prikryl\WinSCP 2\