  The magnetic insulator Gd2Sn2O7 is one of many geometrically frustrated
magnetic materials known to exhibit a nonzero muon spin polarization relaxation
rate, $\lambda(T)$, down to the lowest temperature (T) studied. Such behaviour
is typically interpreted as a significant level of persisting spin dynamics
(PSD) of the host material. In the case of Gd2Sn2O7, such PSD comes as a
surprise since magnetic specific heat measurements suggest conventional gapped
magnons, which would naively lead to an exponentially vanishing $\lambda(T)$ as
$T \rightarrow 0$. In contrast to most materials that display PSD, the ordered
phase of Gd2Sn2O7 is well characterized and both the nature and the magnitude
of the interactions have been inferred from the magnetic structure and the
temperature dependence of the magnetic specific heat. Based on this
understanding, the temperature dependence of the muon spin polarization
relaxation through the scattering of spin waves (magnons) is calculated. The
result explicitly shows that, despite the unusual extensive number of weakly
dispersive (gapped)excitations characterizing Gd2Sn2O7, a remnant of the zero
modes of the parent frustrated pyrochlore Heisenberg antiferromagnet, the
temperature dependence of the calculated $\lambda(T)$ differs dramatically from
the experimental one. Indeed, the calculation conforms to the naive expectation
of an exponential collapse of $\lambda(T)$ at temperatures below ~ 0.7K. This
result, for the first time, illustrates crisply and quantitatively the paradox
that presents itself with the pervasive occurrence of PSD in highly frustrated
magnetic systems as evinced by muon spin relaxation measurements.
