What voltage are you using? It looks like #4 dropped below the threshold voltage needed to produce.
1 = -+ works ok but over 160 Degrees at 21 amps - get about 0.7 LPM
2 = -N+ works near same as one
3 = -NN+ and 20 amp - 120 Deg and 1.4 LPM === at 28A - 1.8 LPM
4 = -NNNNN++NNNNN- 30A - 0.8 LPM
all at 12.2 - 12.7V
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And lots of KOH (16 LBS)
Not currently running HHO.
I dont run HHO during winter.