Hello,
The problem may occur when you switch between themes in Appearance -> Themes is that widgets may lose their positions. It is a WordPress behavior and we are not able to fix this in our theme scope. Now, you need to go to Appearance -> Widgets and move all widgets to appropriate positions.
As a workaround, you can backup your widgets configurations using this plugin https://wordpress.org/plugins/widget-importer-exporter/
Regards
.