In some cases, some contacts may be missing after splitting the VCF file. This usually shows that the splitting of the VCF file was not done well. This problem mostly occurs when you are splitting your VCF file by yourself. It can also be the case that despite your assumptions that your file does not have any problems, some of your contacts may be missing because of improper formatting, such as the absence of tags like BEGIN:VCARD and END:VCARD, improper versions of vCard, etc.
It is recommended in this case that you should not be splitting your VCF file yourself. You should use a correct VCF file splitter that does not delete any of the contacts. I encountered the same problem, and I fixed it by using the GainTools Address Book Manager. It supports bulk VCF splitting and maintains full contact structure. Also, always test a few split files before importing to ensure all contacts appear correctly.
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