Memory leaks are when scripts are using memory without needing it, such as variables that are only used once or not disconnecting events that don’t exist anymore. If you want a more in depth explanation click here and here.
Unhandled objects are the same way as memory leaks but not with variables and such but rather with instances like parts. For example, a script that is making 1000 parts for no reason would be 1000 unhandled objects. Nothing happened to them besides being created. The more instances Roblox needs to handle the lag the game will receive.
These might not be the cause to the problem you are having but it is still good to check. Hopefully you get your game running a little bit better soon.