The second diagnostic build seems to get a little further along than the rest (see below):
2021-11-08 21:30:59,474 [21156-main] INFO VASSAL.launch.StartUp - Starting
2021-11-08 21:30:59,477 [21156-main] INFO VASSAL.launch.StartUp - OS Windows 10 10.0 amd64
2021-11-08 21:30:59,477 [21156-main] INFO VASSAL.launch.StartUp - Java version 17
2021-11-08 21:30:59,477 [21156-main] INFO VASSAL.launch.StartUp - Java home C:\Program Files\VASSAL-3.6.0-SNAPSHOT-739a342c9\jre
2021-11-08 21:30:59,477 [21156-main] INFO VASSAL.launch.StartUp - VASSAL version 3.6.0-SNAPSHOT-739a342c9
2021-11-08 21:30:59,742 [21156-AWT-EventQueue-0] INFO VASSAL.launch.ModuleManager - Manager
2021-11-08 21:31:26,964 [21156-AWT-EventQueue-0] INFO VASSAL.launch.Player$PromptLaunchAction - 1
2021-11-08 21:31:26,964 [21156-AWT-EventQueue-0] INFO VASSAL.launch.AbstractLaunchAction - promptForFile 1
2021-11-08 21:31:26,964 [21156-AWT-EventQueue-0] INFO VASSAL.launch.AbstractLaunchAction - promptForFile 2
2021-11-08 21:31:26,964 [21156-AWT-EventQueue-0] INFO VASSAL.launch.AbstractLaunchAction - promptForFile 3
Seriously, I am beginning to think that my OS (Windows 10) doesn't play well with VASSAL.