What causes the following error？Assertion `idx_map[act] >= 0...’

This problem always occurs when the program is executed. I don’t know if it is a problem with my own data and how to avoid it？
**QNet::SetupGraphInput(std::vector<int>&, std::vector<std::shared_ptr<Graph> >&, std::vector<std::vector<int>*>&, const int*): Assertion `idx_map[act] >= 0 && act >= 0 && act <g->num_nodes' failed.**
_**idx_map[act]=-1**_

