I need to know why MDS failover for a SharePoint page is triggered.
In the browser address bar I see start.aspx when loading a page (as expected), then the browser is redirected to the actual page URL (without start.aspx). That means the MDS engine detected a page that cannot be served via MDS.
Now I need to know why this happens. I remember some time in the past seeing lots of MDS-related debug messages in the browser console. But if I look today (SP 2016) there is nothing.
How can I see/enable debug output for MDS to have more insight into what is happening?