Dork Age: The Dandy Xtreme era (2007-2010) is almost universally considered this, due to the lack of comic content, poorly put together "features" that come off as patronising, and the whole feel of the comic being Two Decades Behind. Some consider the glossy era (2004-2007) as being this as well, with the way it tried too hard to be cool, and requiring a minimum of about three pages to get across a story that could have been told in a single page.
Seasonal Rot: The 1970s, while considered a golden age for the comic by some, is often seen as a weak point in The Dandy's history due to how badly the comic fell behind the times, with outdated strips like Black Bob and Winker Watson running in an era where other comics had more relateable, down to earth strips like Dennis the Menace. To add to this, most people drawing the strips were veteran artists who had started with comics in the 1940s or before. If an artist died, then more often than not their strips were reprinted, rather than replaced or given a new artist. Little effort was made to remedy this until Albert Barnes, who had been the Dandy editor since its inception in the 1930s, was finally replaced... in 1982.