Tracing infection

On batch 10 I did a northern brown ale with London ale. Not sure if it was me willing it to be decent but some seemed ok while others wwere worse clove kinda tastes, thin, and not as flavorful as I expected however athough it wasnt good it wasn’t horrible or blatantly infected. I also thought maybe I just don’t like London ale.

On batch 14 a dark mild I used the London ale yeast I had harvested thinking the infection happened at bottling. No signs of infection during fermentation bottled at 1.008. Ive since stepped up up bottle washing oxy soak, blast with bottle washer, hit with starsan so i know its not bottling now. This batch is clearly infected, after 3 weeks in bottle everyone gushes and the off tastes the brown had are way worse.

My theory is the origional starter got a bug that slowly took over? If that’s the case would it be possible that some of the brown ale bottles were less infected than others?

Is the off taste you’re getting similar to a sour green apple taste by any chance?