I performed nanopore sequencing on human DNA and ran the Nanopore structural variant calling pipeline (miminmap2 + sniffles) against hg38. I loaded the VCF file into IGV and was surprised to see more than two alleles for most of my chromosomes (especially in the centeromeric regions). What does it mean to have > 2 alleles for a region? Is it simply a SV calling error? Or is a there a problem with the way IGV displays VCF tracks? Thanks!