When checking the VRChat website for the list of members to a VRChat group, filtering by role, and loading each page of results, some users are listed multiple times whereas others are not listed at all even though they have the correct role.
Searching for the missing accounts does show them and shows they have the role used for the filter.
This likely happens without filtering by role as well however I checked a small group I own (41 members) and couldn't replicate this. Another group (1600 members) has this problem. It is unclear how many people have the role I was filtering for however it should be less than 100.