In case if you have some problems related to multiplayer in Stellaris PC this article will help you to solve all related problems. Right click the Steam icon and press Settings, where you will have to choose Download. Locate there Drop down file and choose US Los Angeles.
This solution 100% works while the hosts do it or players joining. It is necessary to implement such solution for both host and client to work, so everyone uses this action as a temporary solution. You can use this fix for multiplayer issues untils the developers will bring right solutions that will work without any problems.