Jetpack disables responsive property of theme

I’m using Magazine Basic which is a responsive theme. When I installed Jetpack and added some pics widgets to the side bars, the responsive property did not work anymore – adjust of browser window messed up the contents. It looks like the side bar widgets are fixed and are not resizing automatically with the window together.

Are there any rules regarding the side bar widget pictures (e.g. size) or is this a simple conflict between the plugin and theme settings?

https://www.ads-software.com/plugins/jetpack/