Try fiddling with some of the settings. Possibly this is caused by the YYYY vs yyyy setting, just a guess.
Just now I have imported this in mydemoversion8, Mx 8.17.0, and got it up and running with no issues.
If you have javascript skills than you can try and solve the problem yourself by opening the /widgets/MonthandYearPicker.mpk in your favorite javascript-editor (VisualStudio Code perhaps)
If that is not an option, you best contact the widget builders via the appstore. Maybe they can help.