It might not be related at all, but you should try Enabling the newest Sleeping Part that is currently in Beta : [Beta - Test Me!] Sleeping Part Behavior Improvements
if this works, then this means your issue will be automatically fixed in Online mode in perhaps a few months, if no large scale issue occurs.
It isn’t lag, the brick physics gets stuck because it’s tries to optimize the fall(?) due that it assume nobody is around and seeing it, therefore having a odd rendering,
However, parts that are close to you will be rendered and taken in charge by the client (You) automatically if you’re the closest player to it, object’s physics is temporarily the propriety of the user, also i believe it can be manually set to a chosen player via script.