missing SNPs

[JingjingBai2021]

Hi,
I am trying to predict the HLA-B using the pre-fitted model and got the following output.
I do not understand why there are 72.6% missing SNPs for the Pos+Allele matching type. Is that a normal phenomenon, given the highly polymorphic properties in HLA regions?

My raw dataset was genotyped using Global Screening Array and I used the corresponding model.

Thank you in advance.

###############Output#########
HIBAG model for HLA-B:
500 individual classifiers
791 SNPs
88 unique HLA alleles: 07:02, 07:04, 07:05, ...
Prediction:
based on the averaged posterior probabilities
Model assembly: hg19, SNP assembly: hg19
Matching the SNPs between the model and the test data:
match.type="--" missing SNPs #
Position 26 (3.3%) being used [1]
Pos+Allele 574 (72.6%)* [2]
RefSNP+Position 27 (3.4%)
RefSNP 27 (3.4%)
[1]: useful if ambiguous strands on array-based platforms
[2]: suggested if the model and test data have been matched to the same reference genome
Model platform: Illumina 1M Duo / Infinium Global Screening Array
of SNP loci with flipped alleles: 367
of SNP loci with swapped strands: 365
of samples: 4050
CPU flags: 64-bit
of threads: 8