  A recent zero-field (ZF) and longitudinal-field (LF) muon spin relaxation
($\mu$SR) study of YBa$_2$Cu$_3$O$_y$ [Jian~Zhang {\it et al.},
arXiv:1709.06799] claims to have detected critical slowing down of magnetic
fluctuations near the pseudogap temperature $T^*$, and attribute this to the
onset of slow fluctuating domains of intra-unit-cell magnetic order. Here it is
argued that the relaxation data displayed in this study are misleading due to
an improper account of the nuclear dipole contribution and a failure to
acknowledge the occurrence of muon diffusion.
