  There are emerging tensions for theory results of the hadronic vacuum
polarization contribution to the muon anomalous magnetic moment both within
recent lattice QCD calculations and between some lattice QCD calculations and
R-ratio results. In this paper we work towards scrutinizing critical aspects of
these calculations. We focus in particular on a precise calculation of
Euclidean position-space windows defined by RBC/UKQCD that are ideal quantities
for cross-checks within the lattice community and with R-ratio results. We
perform a lattice QCD calculation using physical up, down, strange, and charm
sea quark gauge ensembles generated in the staggered formalism by the MILC
collaboration. We study the continuum limit using inverse lattice spacings from
$a^{-1}\approx 1.6$ GeV to $3.5$ GeV, identical to recent studies by
FNAL/HPQCD/MILC and Aubin et al. and similar to the recent study of BMW. Our
calculation exhibits a tension for the particularly interesting window result
of $a_\mu^{\rm ud, conn.,isospin, W}$ from $0.4$ fm to $1.0$ fm with previous
results obtained with a different discretization of the vector current on the
same gauge configurations. Our results may indicate a difficulty related to
estimating uncertainties of the continuum extrapolation that deserves further
attention. In this work we also provide results for $a_\mu^{\rm
ud,conn.,isospin}$, $a_\mu^{\rm s,conn.,isospin}$, $a_\mu^{\rm SIB,conn.}$ for
the total contribution and a large set of windows. For the total contribution,
we find $a_\mu^{\rm HVP~LO}=714(27)(13) 10^{-10}$, $a_\mu^{\rm
ud,conn.,isospin}=657(26)(12) 10^{-10}$, $a_\mu^{\rm
s,conn.,isospin}=52.83(22)(65) 10^{-10}$, and $a_\mu^{\rm
SIB,conn.}=9.0(0.8)(1.2) 10^{-10}$, where the first uncertainty is statistical
and the second systematic. We also comment on finite-volume corrections for the
strong-isospin-breaking corrections.
