I don't think you need the text area autogrow widget any more - a normal text area has the option under properties to autogrow, which makes this widget redundant.
Hi David, I do think you are right and this can indeed cause a blank page. As you are using this widget a lot, anything other than upgrading this widget will be a real pain. I will have a look if I can fix this widget for you and keep you posted.
Update I've ported the widget to Mx6. Please test if the widget still works as expected for your use case(s). You can find the widget here: https://github.com/mendix/TextareaAutogrow/blob/master/test/widgets/TextareaAutogrow.mpk
In case you encounter any issues, post them here: https://github.com/mendix/TextareaAutogrow/issues
Hopefully this enables you to focus on the rest of your conversion first, and update your project with more suitable widgets from there.