In fact the knight bus allocates you randomly to Hogwarts fortresses. It seems the number of Hogwarts fortresses is fixed, so when few people take the bus (which is common outside events), they are disseminated amongst those fortresses and it is hard to meet anyone. You can try to quit the fortress and take the bus again which will allocate you to another fortress... until you actually find a busy one...
Comments
This isn't a bug.
In fact the knight bus allocates you randomly to Hogwarts fortresses. It seems the number of Hogwarts fortresses is fixed, so when few people take the bus (which is common outside events), they are disseminated amongst those fortresses and it is hard to meet anyone. You can try to quit the fortress and take the bus again which will allocate you to another fortress... until you actually find a busy one...
This is already discussed as feature request (adapt number of open knight bus fortresses to number of active players in the bus to maintain acceptable player density) here : https://community.harrypotterwizardsunite.com/en/discussion/8799/hard-to-fill-fortress-chambers#latest