A dirty workaround is:

  Solve[eqn == 0, x]

without Reals in Solve.

I know, Gianluca. I prefer Echo since it makes the code and the output more readable. And since I can easily disable it globally by:

$ContextPath = Prepend[$ContextPath, "myContext`"];
Echo[any___] := Null;

Actually I use my own echo-function with takes a global variable testLvl that controls which Echo-output shall be produced.

This works indeed, Mariusz (within 0,06 secs). But why? I had never thought that solving in Complex would be easier than within Reals. But anyway this is a valid solution. I can apply the Reals-condition later to the result.