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I am trying to perform an ionic relaxation, and the structure's ionic positions are effectively converged (and the average force is consistently very low), but convergence is difficult or near-impossible because the net magnetic moment slowly but gradually is decreasing with each ionic step for some reason. Does anyone know why this would be or how I can increase the rate of convergence? It does not get better with different optimization algorithms. The energy is monotonically decreasing, but it is doing so very slowly because the energy difference is mainly a result of the changing net magmom, not any significant change in the atomic positions.

INCAR:
SIGMA = 0.010000
EDIFF = 1.00e-04
EDIFFG = -3.00e-02
PREC = Accurate
GGA = PE
ALGO = All
ISMEAR = 0
NELM = 250
IBRION = 1
ISYM = 0
NELMIN = 6
ISIF = 2
NSW = 500
LORBIT = 11
NCORE = 24
IVDW = 12
LCHARG = .FALSE.
LWAVE = .TRUE.
LREAL = .FALSE.
ISPIN = 2

Snapshot of convergence:
1 E: -1697.927688 SCF: 72 Avg|F|: 0.012 Max|F|: 0.111 Mag: -0.95
2 E: -1697.929517 SCF: 20 Avg|F|: 0.021 Max|F|: 0.141 Mag: -0.94
3 E: -1697.929916 SCF: 16 Avg|F|: 0.016 Max|F|: 0.153 Mag: -0.93
4 E: -1697.929774 SCF: 13 Avg|F|: 0.015 Max|F|: 0.153 Mag: -0.93
5 E: -1697.930294 SCF: 7 Avg|F|: 0.015 Max|F|: 0.106 Mag: -0.93
6 E: -1697.931108 SCF: 14 Avg|F|: 0.012 Max|F|: 0.116 Mag: -0.93
7 E: -1697.931391 SCF: 11 Avg|F|: 0.012 Max|F|: 0.129 Mag: -0.93
8 E: -1697.931642 SCF: 9 Avg|F|: 0.011 Max|F|: 0.074 Mag: -0.93
9 E: -1697.931804 SCF: 13 Avg|F|: 0.017 Max|F|: 0.187 Mag: -0.94
10 E: -1697.932352 SCF: 9 Avg|F|: 0.015 Max|F|: 0.276 Mag: -0.93
11 E: -1697.932486 SCF: 8 Avg|F|: 0.015 Max|F|: 0.138 Mag: -0.93
12 E: -1697.932545 SCF: 11 Avg|F|: 0.016 Max|F|: 0.196 Mag: -0.93
13 E: -1697.933086 SCF: 8 Avg|F|: 0.014 Max|F|: 0.149 Mag: -0.93
14 E: -1697.933210 SCF: 15 Avg|F|: 0.016 Max|F|: 0.141 Mag: -0.92
15 E: -1697.933675 SCF: 12 Avg|F|: 0.017 Max|F|: 0.174 Mag: -0.93
16 E: -1697.933902 SCF: 10 Avg|F|: 0.013 Max|F|: 0.102 Mag: -0.92
17 E: -1697.933857 SCF: 16 Avg|F|: 0.021 Max|F|: 0.194 Mag: -0.92
18 E: -1697.935457 SCF: 14 Avg|F|: 0.015 Max|F|: 0.121 Mag: -0.92
19 E: -1697.935777 SCF: 10 Avg|F|: 0.011 Max|F|: 0.107 Mag: -0.92
20 E: -1697.935717 SCF: 17 Avg|F|: 0.025 Max|F|: 0.216 Mag: -0.92
21 E: -1697.936702 SCF: 14 Avg|F|: 0.013 Max|F|: 0.099 Mag: -0.92
22 E: -1697.937002 SCF: 15 Avg|F|: 0.023 Max|F|: 0.169 Mag: -0.92
23 E: -1697.938252 SCF: 13 Avg|F|: 0.012 Max|F|: 0.077 Mag: -0.92
24 E: -1697.938545 SCF: 19 Avg|F|: 0.020 Max|F|: 0.246 Mag: -0.92
25 E: -1697.940213 SCF: 11 Avg|F|: 0.012 Max|F|: 0.104 Mag: -0.91
26 E: -1697.940266 SCF: 11 Avg|F|: 0.014 Max|F|: 0.113 Mag: -0.92
27 E: -1697.941244 SCF: 15 Avg|F|: 0.014 Max|F|: 0.132 Mag: -0.91
28 E: -1697.941915 SCF: 10 Avg|F|: 0.011 Max|F|: 0.084 Mag: -0.91
29 E: -1697.942095 SCF: 10 Avg|F|: 0.011 Max|F|: 0.210 Mag: -0.91
30 E: -1697.943434 SCF: 17 Avg|F|: 0.018 Max|F|: 0.176 Mag: -0.90
31 E: -1697.943556 SCF: 12 Avg|F|: 0.015 Max|F|: 0.192 Mag: -0.90
32 E: -1697.942000 SCF: 20 Avg|F|: 0.037 Max|F|: 0.390 Mag: -0.90
33 E: -1697.945232 SCF: 14 Avg|F|: 0.019 Max|F|: 0.170 Mag: -0.90
34 E: -1697.938518 SCF: 25 Avg|F|: 0.046 Max|F|: 0.819 Mag: -0.88
35 E: -1697.946915 SCF: 14 Avg|F|: 0.017 Max|F|: 0.198 Mag: -0.89
36 E: -1697.945629 SCF: 20 Avg|F|: 0.034 Max|F|: 0.493 Mag: -0.89
37 E: -1697.948437 SCF: 12 Avg|F|: 0.015 Max|F|: 0.139 Mag: -0.89
38 E: -1697.948413 SCF: 20 Avg|F|: 0.027 Max|F|: 0.270 Mag: -0.89
39 E: -1697.949167 SCF: 17 Avg|F|: 0.017 Max|F|: 0.212 Mag: -0.89
40 E: -1697.949657 SCF: 9 Avg|F|: 0.016 Max|F|: 0.144 Mag: -0.89
41 E: -1697.949665 SCF: 15 Avg|F|: 0.019 Max|F|: 0.275 Mag: -0.89
42 E: -1697.950981 SCF: 11 Avg|F|: 0.015 Max|F|: 0.117 Mag: -0.89
43 E: -1697.950775 SCF: 7 Avg|F|: 0.021 Max|F|: 0.237 Mag: -0.89
44 E: -1697.951441 SCF: 9 Avg|F|: 0.015 Max|F|: 0.149 Mag: -0.89
45 E: -1697.950013 SCF: 17 Avg|F|: 0.026 Max|F|: 0.425 Mag: -0.90
46 E: -1697.952697 SCF: 14 Avg|F|: 0.015 Max|F|: 0.139 Mag: -0.89

For anyone with similar issues, I needed to decrease EDIFF to 1e-6 for many of my materials of interest to achieve ionic convergence with IBRION = 1. Using IBRION = 2 resulted in ZBRENT issues because of the nearly converged ionic positions, but the forces weren't accurate enough with IBRION = 1 when using EDIFF = 1e-4. That doesn't solve the magnetic moment issue as a function of ionic step, but VASP support kindly recommended that I suggest tweaking the magnetic moment mixing tags, which I am currently investigating.

I would not regard a maximum |F| of 0.139 as negligible, therefore I rather think it is the ionic positions
with are not fully converged, not the magnetic moments