Currently, we have a local test net with 4 substrate nodes using this runtime which has the staking and session pallets. 2 nodes (Alice and Bob) are validators, placed in the chain spec json file and the other 2 (Charlie and Dave) were added as waiting validators while the chain was running with the goal to be chosen to the next session, but this never occurs. In each new epoch, the same validators (Alice and Bob) take place and I did not notice any session change event on polkadot JS UI. I would like to know if I'm missing some configuration or action to add new validators in a running network?
This issue have been solved in this PR- https://github.com/ChainSafe/substrate-node-template/pull/4