Issue: The widget content is lost completely when you migrate WP Site with the Generate Theme. For example site is on local server then need to move to client’s server. After doing that the widget content is completely gone.
Or even if you have to swap themes for troubleshooting. I noticed that with, for example: Twenty-Twelve theme, the widgets would just appear in Inactive Widgets. Try it out and let me know if you get the same results.
Try placing a text widget in the Footer Widgets. Activate another theme then switch back.
Cheers!