From the vcf file, the field description is:

##INFO=<ID=AS_SB_TABLE,Number=1,Type=String,Description="Allele-specific forward/reverse read counts for strand bias tests. Includes the reference and alleles separated by |.">

An example of this field is AS_SB_TABLE=1067,529|5,196. However, readVcf seems to split by , and take only the first number (1067) - this is what I see in R:

> m2crct = readVcf('somatic_mutect2.filtered.vcf.gz')
> head(info(m2crct)$AS_SB_TABLE)
[1] "1067" "10"   "56"   "49"   "37"   "192"

I think it's a bug in readVcf, not in GATK - in the field description it is stated that it should be a String and have one element (Number=1). So it should not be split by ,. Comma can be part of a string, and number of items should be validated (one should expect one item in this case, which is the whole arbitrary string.)

> sessionInfo()
R version 4.2.2 (2022-10-31)
Platform: x86_64-apple-darwin17.0 (64-bit)
Running under: macOS Big Sur 11.7.2

Matrix products: default
LAPACK: /Library/Frameworks/R.framework/Versions/4.2/Resources/lib/libRlapack.dylib

locale:
[1] en_US.UTF-8/en_US.UTF-8/en_US.UTF-8/C/en_US.UTF-8/en_US.UTF-8

attached base packages:
[1] stats4    stats     graphics  grDevices utils     datasets  methods   base     

other attached packages:
 [1] VariantAnnotation_1.44.0    Rsamtools_2.14.0            Biostrings_2.66.0           XVector_0.38.0             
 [5] SummarizedExperiment_1.28.0 Biobase_2.58.0              GenomicRanges_1.50.2        GenomeInfoDb_1.34.9        
 [9] IRanges_2.32.0              S4Vectors_0.36.1            MatrixGenerics_1.10.0       matrixStats_0.63.0         
[13] BiocGenerics_0.44.0        

loaded via a namespace (and not attached):
 [1] Rcpp_1.0.9               lattice_0.20-45          prettyunits_1.1.1        png_0.1-8               
 [5] assertthat_0.2.1         digest_0.6.31            utf8_1.2.2               BiocFileCache_2.6.0     
 [9] R6_2.5.1                 RSQLite_2.2.20           httr_1.4.4               pillar_1.8.1            
[13] zlibbioc_1.44.0          rlang_1.0.6              GenomicFeatures_1.50.4   progress_1.2.2          
[17] curl_5.0.0               rstudioapi_0.14          blob_1.2.3               Matrix_1.5-1            
[21] BiocParallel_1.32.5      stringr_1.5.0            RCurl_1.98-1.9           bit_4.0.5               
[25] biomaRt_2.54.0           DelayedArray_0.24.0      rtracklayer_1.58.0       compiler_4.2.2          
[29] pkgconfig_2.0.3          tidyselect_1.2.0         KEGGREST_1.38.0          tibble_3.1.8            
[33] GenomeInfoDbData_1.2.9   codetools_0.2-18         XML_3.99-0.13            fansi_1.0.3             
[37] crayon_1.5.2             dplyr_1.0.10             dbplyr_2.3.0             GenomicAlignments_1.34.0
[41] bitops_1.0-7             rappdirs_0.3.3           grid_4.2.2               lifecycle_1.0.3         
[45] DBI_1.1.3                magrittr_2.0.3           cli_3.6.0                stringi_1.7.12          
[49] cachem_1.0.6             xml2_1.3.3               ellipsis_0.3.2           filelock_1.0.2          
[53] vctrs_0.5.1              generics_0.1.3           rjson_0.2.21             restfulr_0.0.15         
[57] tools_4.2.2              bit64_4.0.5              BSgenome_1.66.2          glue_1.6.2              
[61] hms_1.1.2                yaml_2.3.6               parallel_4.2.2           fastmap_1.1.0           
[65] AnnotationDbi_1.60.0     memoise_2.0.1            BiocIO_1.8.0