Error: Timeout waiting for WinSCP to respond - WinSCP has not responded in time - 5.7.5

Daily scheduled task running PowerShell script to perform SFTP upload. Frequently (but not always) errors out with "Timeout waiting for WinSCP to respond - WinSCP has not responded in time (response log file blabla.tmp was not created)". We know it's not permission issues since it does run successfully more than half of the time.

Server is 2008 R2
WinSCP version 5.7.5 with .NET library file 1.2.9.5665 (part of version 5.7.5).

Recently upgraded from 5.5.6 (and rebooted) but it hasn't made a difference.

Any tips on troubleshooting this further?

Please attach a full debug log files showing both the successful and failed run.

Here's a debug log from both a successful job and a failure. It took a while because it actually hadn't failed in a few days.

The system seems to be under a heavy load.
Can you try to set the Session.Timeout to higher value?

I've increased the timeout from 2 minutes to 5. I'll see if that makes a difference.

$WinSCPconfig.TimeoutInMilliseconds = 300000