  There are expected to be $\sim 10^8$ isolated black holes (BHs) in the Milky
Way. OGLE-2011-BLG-0462/MOA-2011-BLG-191 (OB110462) is the only such BH with a
mass measurement to date. However, its mass is disputed: Lam et al. (2022a,b)
measured a lower mass of $1.6 - 4.4 M_\odot$, while Sahu et al. (2022);
Mr\'{o}z et al. (2022) measured a higher mass of $5.8 - 8.7 M_\odot$. We
re-analyze OB110462, including new data from the Hubble Space Telescope (HST)
and re-reduced Optical Gravitational Lensing Experiment (OGLE) photometry. We
also re-reduce and re-analyze the HST dataset with newly available software. We
find significantly different ($\sim 1$ mas) HST astrometry than Lam et al.
(2022a,b) in the de-magnified epochs due to the amount of positional bias
induced by a bright star $\sim$0.4 arcsec from OB110462. After modeling the
updated photometric and astrometric datasets, we find the lens of OB110462 is a
$6.0^{+1.2}_{-1.0} M_\odot$ BH. Future observations with the Nancy Grace Roman
Space Telescope, which will have an astrometric precision comparable or better
to HST but a field of view $100\times$ larger, will be able to measure hundreds
of isolated BH masses via microlensing. This will enable the measurement of the
BH mass distribution and improve understanding of massive stellar evolution and
BH formation channels.
