Hello Fabsn and all,
I am new to Muse, but in the process of setting up a web site for a client I encountered the same issue. I created the desktop, and then the mobile versions of the site with no problems, but after I added the tablet that is the only version my laptop running IE 11 would display. I thought I had done something wrong, so I went back into Muse. The first thing I noticed was the main master page for desktop had somehow inherited the dimensions of the same master page for tablet. I corrected the dimensions, and then to avoid confusion I added -[platform] to the names of each master page for each platform. I verified the previews in Muse and then re-published. Now my laptop is loading the desktop version as it should.
In summary I believe the issue, in my case anyway, was the master page dimension changes I noted.
Hope my experience helps!