  Follow-up observations of high-magnification gravitational microlensing
events can fully exploit their intrinsic sensitivity to detect extrasolar
planets, especially those with small mass ratios. To make followup more uniform
and efficient, we develop a system, HighMagFinder, based on the real-time data
from the Korean Microlensing Telescope Network (KMTNet) to automatically alert
possible ongoing high-magnification events. We started a new phase of follow-up
observations with the help of HighMagFinder in 2021. Here we report the
discovery of two planets in high-magnification microlensing events,
KMT-2021-BLG-0171 and KMT-2021-BLG-1689, which were identified by the
HighMagFinder. We find that both events suffer the ``central-resonant'' caustic
degeneracy. The planet-host mass-ratio is $q\sim4.7\times10^{-5}$ or $q\sim
2.2\times10^{-5}$ for KMT-2021-BLG-0171, and $q\sim2.5\times10^{-4}$ or $q\sim
1.8\times10^{-4}$ for KMT-2021-BLG-1689. Together with two events reported by
Ryu et al. (2022), four cases that suffer such degeneracy have been discovered
in the 2021 season alone, indicating that the degenerate solutions may have
been missed in some previous studies. We also propose a new factor for
weighting the probability of each solution from the phase-space. The resonant
interpretations for the two events are disfavored under this consideration.
This factor can be included in future statistical studies to weight degenerate
solutions.
