Hello,
The problem that 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/
To fix the logo problem, you need to open your SVG file with some editor like Sublime Text or default system text editor and add height and width attributes to your svg tag like it is shown on the screenshot https://gyazo.com/83fd36b0bb9628bb1aed2bd3d5d063c5
Then you will need to reupload your logo in WordPress Dashboard.
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