Here is an example of a test page with one breakpoint I have created some time ago.
I imported the site created in Adobe Muse 2017.0 and converted the Muse file to version 2018.1
The layout worked so far in Adobe Muse 2017.0. Since 2018.1 the layout is broken.
Here is the test page to view an example.
For whatever reason the image on the left will be cropped.
I guess the Adobe Muse Team has a lot of WORK TO DO till 2020 with their EXTENDED MUSE SUPPORT.