I have combined 400 gVCFs into two files (S2_200_F1.g.vcf.gz and S2_200_F2.g.vcf.gz), each one includes 200 samples. I am trying to but failed to combine these two files. The error info is Unexpected base in allele bases '*CG'.

I was wondering how do I fix this error by working on g.vcf.gz files, instead of going back to bam files as suggested by https://gatk.broadinstitute.org/hc/en-us/community/posts/360071826651-GATK4-1-3-0-HaplotypeCaller-ERROR ?

a) GATK version used: GATK 4.0.3.0
b) Exact command used:

time gatk --java-options "-Xmx90G" CombineGVCFs \
-R b37_human_g1k_v37_decoy.fasta \
--Variant S2_200_F1.g.vcf.gz \
--variant S2_200_F2.g.vcf.gz \
-O S2_all.g.vcf.gz

c) Entire error log:

12:26:50.512 INFO  CombineGVCFs - Done initializing engine
12:27:20.968 INFO  ProgressMeter - Starting traversal
12:27:20.968 INFO  ProgressMeter -        Current Locus  Elapsed Minutes    Variants Processed  Variants/Minute
12:28:37.418 INFO  ProgressMeter -              1:16712              1.3                  1000            784.8
12:29:33.168 INFO  ProgressMeter -              1:24589              2.2                  3000           1361.6
12:30:03.475 INFO  ProgressMeter -              1:65581              2.7                  5000           1846.1
12:30:15.035 INFO  ProgressMeter -              1:69504              2.9                  6000           2068.2
12:31:16.751 INFO  ProgressMeter -             1:120843              3.9                  7000           1781.3
12:31:27.904 INFO  ProgressMeter -             1:639065              4.1                 11000           2672.8
12:32:27.876 INFO  ProgressMeter -             1:664208              5.1                 13000           2541.5
12:33:04.896 INFO  ProgressMeter -             1:703850              5.7                 14000           2442.4
12:33:18.757 INFO  ProgressMeter -             1:762047              6.0                 18000           3018.5
12:33:19.283 INFO  CombineGVCFs - Shutting down engine
[October 1, 2021 12:33:19 PM SGT] org.broadinstitute.hellbender.tools.walkers.CombineGVCFs done. Elapsed time: 6.58 minutes.
Runtime.totalMemory()=9969860608
java.lang.IllegalArgumentException: Unexpected base in allele bases '*CG'
        at htsjdk.variant.variantcontext.Allele.<init>(Allele.java:165)
        at htsjdk.variant.variantcontext.Allele.create(Allele.java:239)
        at org.broadinstitute.hellbender.tools.walkers.ReferenceConfidenceVariantContextMerger.extendAllele(ReferenceConfidenceVariantContextMerger.java:406)
        at org.broadinstitute.hellbender.tools.walkers.ReferenceConfidenceVariantContextMerger.remapAlleles(ReferenceConfidenceVariantContextMerger.java:178)
        at org.broadinstitute.hellbender.tools.walkers.ReferenceConfidenceVariantContextMerger.merge(ReferenceConfidenceVariantContextMerger.java:70)
        at org.broadinstitute.hellbender.tools.walkers.CombineGVCFs.endPreviousStates(CombineGVCFs.java:340)
        at org.broadinstitute.hellbender.tools.walkers.CombineGVCFs.createIntermediateVariants(CombineGVCFs.java:189)
        at org.broadinstitute.hellbender.tools.walkers.CombineGVCFs.apply(CombineGVCFs.java:134)
        at org.broadinstitute.hellbender.engine.MultiVariantWalkerGroupedOnStart.apply(MultiVariantWalkerGroupedOnStart.java:73)
        at org.broadinstitute.hellbender.engine.VariantWalkerBase.lambda$traverse$0(VariantWalkerBase.java:110)
        at java.util.stream.ForEachOps$ForEachOp$OfRef.accept(ForEachOps.java:184)
        at java.util.stream.ReferencePipeline$2$1.accept(ReferencePipeline.java:175)
        at java.util.Iterator.forEachRemaining(Iterator.java:116)
        at java.util.Spliterators$IteratorSpliterator.forEachRemaining(Spliterators.java:1801)
        at java.util.stream.AbstractPipeline.copyInto(AbstractPipeline.java:481)
        at java.util.stream.AbstractPipeline.wrapAndCopyInto(AbstractPipeline.java:471)
        at java.util.stream.ForEachOps$ForEachOp.evaluateSequential(ForEachOps.java:151)
        at java.util.stream.ForEachOps$ForEachOp$OfRef.evaluateSequential(ForEachOps.java:174)
        at java.util.stream.AbstractPipeline.evaluate(AbstractPipeline.java:234)
        at java.util.stream.ReferencePipeline.forEach(ReferencePipeline.java:418)
        at org.broadinstitute.hellbender.engine.VariantWalkerBase.traverse(VariantWalkerBase.java:108)
        at org.broadinstitute.hellbender.engine.MultiVariantWalkerGroupedOnStart.traverse(MultiVariantWalkerGroupedOnStart.java:118)
        at org.broadinstitute.hellbender.engine.GATKTool.doWork(GATKTool.java:893)
        at org.broadinstitute.hellbender.cmdline.CommandLineProgram.runTool(CommandLineProgram.java:134)
        at org.broadinstitute.hellbender.cmdline.CommandLineProgram.instanceMainPostParseArgs(CommandLineProgram.java:179)
        at org.broadinstitute.hellbender.cmdline.CommandLineProgram.instanceMain(CommandLineProgram.java:198)
        at org.broadinstitute.hellbender.Main.runCommandLineProgram(Main.java:160)
        at org.broadinstitute.hellbender.Main.mainEntry(Main.java:203)
        at org.broadinstitute.hellbender.Main.main(Main.java:289)

Thank you!