@MarcosSpessatto The client-side, for instance, the LivechatDepartmentForm need to stop using the 3rd parameter of the method Livechat.saveDepartment, we need to stop using the departmentAgents parameter here:

, the agents need to be inserted/removed to departments by using a specific method and REST API method for that, so you can control this on the client, for example, when an agent is added, you can create a specific var to store it until the user clicks to save. The same can be done when an agent is deleted. Then, you can apply these changes after the user save the department, did you get it?
The current implementation is overriding the agents of the departments based on the data passed through that parameter, but to give you an example, the Livechat Department form fetches the agents through the REST API with pagination. So, when the department is saved, only those agents passed to the parameter will be affected, which means that if the department has 1k agents and the client sent just the data related to the existing agents on the client-side, the other agents in the collection won't be affected, did you get it?
And there is one more thing: this code is considering only users passed to the parameter agents, and this part of the code is considering this also, so any other existing agents in the collection will be removed.
To fix this, the client needs to add/remove agents through the REST API methods instead of passing changes related to the agents through the method parameters.

Also, we need to remove this process from this part of the code

. To remove agents, we need to use a specific method to perform it, even though we still support creating departments with default agents, like through the REST API method.