The problem might come from outside of the Post Views Counter – most probably your theme or a different plugin is modifying the number format function, which is used by PVC (https://developer.wordpress.org/reference/functions/number_format_i18n/). It is used in order to format the views number for thousands and other larger numbers – that would explain why it gets distorted right after exceeding a given number like 100, 1000 or more.