Frequently hypercyclic operators with irregularly visiting orbits

We prove that a bounded operator $T$ on a separable Banach space $X$ satisfying a strong form of the Frequent Hypercyclicity Criterion (which implies in particular that the operator is universal in the sense of Glasner and Weiss) admits frequently hypercyclic vectors with irregularly visiting orbits, i.e. vectors $x\in X$ such that the set $$\mathcal{N}$_T(x,U)={n\ge 1,;,T^{n}x\in U}$ofreturntimesof$x$into$U$undertheactionof$T$haspositivelowerdensityforeverynon-emptyopenset$U\subseteq X$, but there exists a non-empty open set $U_0\subseteq X$ such that $\text{nt}x{U}_0$ has no density.