When an internal collision is detected, an assert is triggered if there is no packet in the queue.

There are two issues according to me:
1) It does not consider the BA queue;
2) Packets that exceed their maximum lifetime limit are removed from the queue. If a packet is removed between the access request to the manager and the moment the internal collision is detected, this assert is triggered. In that case, the internal collision should actually have no effect on that EdcaTxopN and simulation should keep on running.

See my proposed solution is attachment.