Thanks for your report.
I have sent you an email with a debug version of WinSCP to the address you have used to register on this forum.
Windows 10 Pro (1607, last patched 5/5/17 with KB3150513) with SSD. 5.7.6 started up in ~7 seconds. I upgraded to 5.9.5 and it takes a full 2 minutes or more to show the initial screen. I uninstalled and reinstalled 5.9.3, same problem. Went back to 5.7.6 and it's back to ~7 seconds. This is consistent behavior across 3 different machines with identical configuration.
The Windows task manager shows that WinSCP starts up almost immediately but the screen doesn't display for the 2 minutes+. Almost looks like it's waiting to timeout before displaying the screen. I went through the settings but I couldn't see anything that seemed related.