Currently, on the PSO2 subreddit, users are complaining about a memory leak in the game. This is caused by removing -optimize from the runtime arguments, either directly, or through the use of the third party launcher Tweaker from Arks Layer. DO NOT do this, it is there for a reason. The current good work around for the lobby stuttering is to rename pso2.exe to pso2launcher.exe and run the game that way. Until the stuttering is fixed officially, or a better work around is found, do NOT remove the -optimize arguement, do NOT set DisableMemoryOptimize to true in the user.pso2 file, and do NOT use the Tweaker's lobby fix (as it does the same as the previous 2). Also, do not report this problem here or to the Twitter account, as this is caused by a user error, not by coding issues. I'd honestly recommend not using Tweaker at all at this point, because none of the releases they've posted has been through any kind of actual testing, and it shows. And never mess with stuff when you don't know what it does!
SEGA does not officially support Tweaker, however they've shown in the past that they don't care about it being used to access the game, even apologizing for game guard blocking it at one point. Personally, I'd only recommend using something like this when its been properly tested completely, and is known to be working (Due to how logging into the game works, Tweaker does NOT access your account information, it just launches the game in a different way that bypasses some of the problems). Recent Errors of note also caused by Tweaker: Dumping/Corrupting permissions tables for the game folders (NA version), breaking the install by conflicting with the Microsoft Store, causing the Microsoft store to dump the files and reinstall because it thinks there's an error.