Hey BMJ, sorry for not getting back to you sooner. I can't reproduce the issue with the "save game" block in build 9785 on Windows 7; my best guess would be that it does have something to do with Windows 10. It's extremely weird that this block wouldn't work, as it translates to the same code as the built-in block. Does the same issue occur with the built-in "save game" block?
To both of you, I've created a new and improved version of the extension for Stencyl 3.4+. Stencyl considers it a separate extension, so you'll need to manually upgrade the extension on each project (open project, go to Settings > Extensions, enable "Extra Utilities" and disable "Extra Utilities 3.2", save and close project), but it should permanently fix your problems with not being able to see the latest version.