I'm working with 16S amplicon data and my own classifiers I trained with V3-V4 and V1-V2 regions (for meta-analysis).
There is no problem on dada2 and taxonomy profiling steps on QIIME2, and I found out that some samples are assigned with only single species too largely (70~80%) like below (samples surrounded by black square):
Is this a separate dataset compared to what you have been working on here and here? This sounds like a very similar issue to the two linked posts above, so unless this is an entirely new dataset and you are running a different analysis here, please keep your replies within those posts to help us keep things organized on our end. Thanks!