BP on multisite can be quite complicated.
If you network-activated BP, then afaik the users will be available on all ‘blogs’.
There are several ways to config a BP > multisite install.
There are a couple of plugins that may help, for example:
https://buddydev.com/plugins/buddypress-multi-network/
More info from the BP codex:
https://codex.buddypress.org/getting-started/installation-in-wordpress-multisite/