Help! Archaea microbial community

Hello all, I need your help. My samples are soil samples and I have amplified the archaea V6-V8 region from 16S rRNA genes using the following primers.
Ar915aF: TCGTCGGCAGCGTCAGATGTGTATAAGAGACAGAGGAATTGGCGGGGGAGCAC/
Ar1386R: GTCTCGTGGGCTCGGAGATGTGTATAAGAGACAGGCGGTGTGTGCAAGGAGC.

I have been getting problems after I run screen.seqs, my number of sequences gets very low. For example:

mothur > 
summary.seqs(fasta=stability.trim.contigs.unique.align,count=stability.trim.contigs.count_table)

Using 12 processors.

		Start	End	NBases	Ambigs	Polymer	NumSeqs
Minimum:	0	0	0	0	1	1
2.5%-tile:	1044	1062	7	0	2	18492
25%-tile:	28439	42539	272	0	5	184914
Median: 	28439	42539	488	0	5	369827
75%-tile:	28439	42539	490	0	5	554740
97.5%-tile:	43102	43116	492	0	7	721161
Maximum:	43116	43116	500	0	8	739652
Mean:	28266	38971	372	0	4
# of unique seqs:	489714
total # of seqs:	739652

It took 192 secs to summarize 739652 sequences.

Output File Names:
stability.trim.contigs.unique.summary

Then I run

mothur > screen.seqs(fasta=stability.trim.contigs.unique.align,count=stability.trim.contigs.count_table, start=28439, end=43116)

mothur >  summary.seqs(fasta=current, count=current)

Using stability.trim.contigs.good.count_table as input file for the count parameter.
Using stability.trim.contigs.unique.good.align as input file for the fasta parameter.

Using 12 processors.

                Start   End     NBases  Ambigs  Polymer NumSeqs
Minimum:        28439   43116   465     0       5       1
2.5%-tile:      28439   43116   465     0       5       1
25%-tile:       28439   43116   466     0       5       2
Median:         28439   43116   466     0       5       4
75%-tile:       28439   43116   466     0       6       6
97.5%-tile:     28439   43116   466     0       7       7
Maximum:        28439   43116   466     0       7       7
Mean:   28439   43116   465     0       5
# of unique seqs:       7
total # of seqs:        7

It took 0 secs to summarize 7 sequences.

Output File Names:
stability.trim.contigs.unique.good.summary

I am not sure why my number of sequences gets very low. Is there something I can do to fix it? Thank you for all your help!

Can you try using end=42539 in screen.seqs?

Pat