This was obvious to any statistician working in the area, as the same thing happens with gene expression in virtually any tissue. There are also seasonality eff

This was obvious to any statistician working in the area, as the same thing happens with gene expression in virtually any tissue. There are also seasonality effects in gene expression, and even in microbiomes: https://doi.org/10.1126/science.aan4834 https://doi.org/10.1126/science.aan4834 Accounting for these covariates is important. But with larger sample sizes, they might cancel out anyway. IMHO, larger studies will be reproducible. There are other much more serious technical issues.