About six years ago, I began distancing myself from any recommendation on probiotic food or capsule. It's not that I supposed Kombucha increased toxins in the brain but because the 100 trillion symbionts on and in our body are 99% ANAEROBIC, meaning you primarily help them proliferate through the intake of fiber and resistant starches (to feed the beneficial strains) and reduce the intake of refined foods (to starve the baddies).
That said, the dose makes the poison. One of the most difficult concepts to embrace is that no foods or attempted lifestyle behaviors are "good" or "bad." They are productive or unproductive when stacked against all other variables.
Likewise, with this finding, I still wouldn't classify probiotics as bad or worthless, but certainly insufficient AND they carry a risk.
For those who've added in probiotics only to notice no benefit or a possible diminishment of cognitive clarity, it may be worth a reevaluation at this point: https://www.nature.com/articles/s41424-018-0030-7