The website uses the following API endpoint to populate the Group Member List:
groups/{groupId}/members?n=25&offset=0
This endpoint takes in two query params: n (number of users to get) and offset (number of users to skip over before starting to list them).
When this latter offset value is higher than 5,000, an error such as the following is returned:
{"error":{"message":"offset=5100 is much too high․ refine your search you savages․","status_code":400}}
The message in this error code seems to imply that this error was intended to prevent requests of member blocks that are too large. However, this condition is being applied to the offset parameter as well, which is unrelated to the size of the request.
As a result of this, the Group Member List page on the website will stop working after scrolling through 5,000 users.