If you are seeing an error, please provide(REQUIRED) :
a) GATK version used: v4.1.8
b) Exact command used:

gatk HaplotypeCaller -R ../../genome/genome.fa -I Alignment_Germline_Aziz/$i.bam --dbsnp ../../recalset/dbsnp_132.hg19.vcf -L ../../recalset/nextera_dna_exome_targeted_regions_manifest_v1_2.bed -O Output_Germline_Aziz/${i}_HaplotypeCall.vcf -A StrandBiasBySample

c) Entire error log:
No error
If not an error, choose a category for your question(REQUIRED):

one of variant detected is 

chr1 8418596 . C G 244.87 PASS ALLELE_END;ANNOVAR_DATE=2020-06-08;BaseQRankSum=0.118;DP=11;Dels=0;EXON;FC=Missense_E779D,Missense_E1333D,Missense_E1333D;FS=0;GI=RERE,RERE,RERE;HRun=1;HaplotypeScore=0.9469;MQ=60;MQ0=0;MQRankSum=-1.532;QD=22.26;ReadPosRankSum=-0.825;SB=-36.14;TI=NM_001042682,NM_001042681,NM_012102 GT:AD:DP:GQ:PL:MQ:GQX:VF 0/1:2,9:11:45:275,0,45:60:45:0.818

My concern is why the variant caller detected as heterozygous while its VF is 80% and AD=9:11 -> 9 of 11 are altered.

I expect the GT for this variant is homozygous since the VF is 80%!

based on what it decide its heterozygous?

Note: I got same result using unifiedGenotyper and haplotypeCaller.