There are 2 things you can check in this case:
1 - Concurrent calls settings
If your package has the feature queue, under 'settings when open', you can set and update the amount of concurrent calls.
(If you forward the calls to a queue outside our platform, make sure that the number off concurrent calls is according to the amount of available agents)
2 - Agents availability
Ensure your agents set their status as available, otherwise calls are not delivered to them.