Screen.seqs filtering all out - maxambig=0

breast skin swabs - v4 - 16s - 250cycles - paired end
Each sample was PCR amplified with two differently bar coded V4 fusion primers.
For about 30% of my samples, I get about 10 reads left after screen.seqs because of “maxambig=0”
summary after making contigs for one of the samples

What could be going on? Are these just bad data?

Thank you

Looks like bad data, but it is suspicious that so many have exactly 2 ambiguous base calls. Are you using the Kozich method?