The old "secular stagnation" of the 1930s and 1940s was a fear that the world was approaching satiation with respect to things that it would be profitable to build. The new "secular stagnation" is much more a fear of growing monopoly power and a growing desire for safety. It is thus a very different thing—or, rather, two different things happening alongside each other:

Emmanuel Farhi and Francois Gourio: Accounting for Macro-Finance Trends: "Most developed economies have experienced large declines in risk-free interest rates and lacklustre investment over the past 30 years, while the profitability of private capital has increased slightly. Using an extension of the neoclassical growth model, this column identifies what accounts for these developments. It finds that rising market power, rising unmeasured intangibles, and rising risk premia play a crucial role, over and above the traditional culprits of increasing savings supply and technological growth slowdown...