merge error

[Qijie0615]

These two variations were found in four samples, and when I only used this four-sample vcf to merge, these two variations could be merged into one correctly. However, when I merged with a population (vcf with 4000 samples), these two mutations could not be merged into one.
SURVIVOR merge DEL_FileList.list 1000 1 1 1 0 0 repeat.DEL.vcf
Looking forward to your reply！

chr8	84700770	DEL_3417	N		591	PASS	SUPP=1;SVLEN=-36499;SVTYPE=DEL;SVMETHOD=SURVIVOR1.0.7;CHR2=chr8;END=84737242;CIPOS=0,0;CIEND=0,0;STRANDS=+-
chr8	84700556	DEL_3914	N		999	PASS	SUPP=3;SVLEN=-36602;SVTYPE=DEL;SVMETHOD=SURVIVOR1.0.7;CHR2=chr8;END=84737218;CIPOS=0,281;CIEND=0,0;STRANDS=+-