I have a self-hosted server, I and friends can join the server, but we always and instantly server split. We can chat, run some commands, but physically and on the scoreboard, we don’t see each other.
What resources do you run on your server. In addition, it is better to not host a server on your local computer, but purchase a vps or a hosted machine instead, as bad network connection has a huge major influence with timing out and session splits.
The best way would be seeing if you have an issue with a fresh server without any resources. If you don’t get any issues with a fresh plain server, then you could add your resources one by one and seeing what is causing an issue. Although, I still have strong beliefs poor network connection could have a role in this.