Oof. I’m going to screenshot my parts.
Okay, here it is.
These are the bone walls, and they move. They are unioned currently, if I seperate it though, the lag is still seriously bad.
I need to go. If you have ways to help, please do. I’m completely stumped. 
Managed to fix my lag, got no idea if this would work for you but I reset all studio settings to default and it runs well now.
Also if your getting bad lag, try selecting everything and anchoring it.
Okay. Thanks. I will try it. Hope it works.
I think it is because of recent updates (to Studio and Roblox). I checked my old games and they also had very much issues with rendering.
Ok, so you have a ton of moving parts that you are cloning out of ServerStorage and are causing lag issues.
How many tris in the Unions? Unions are horrible for having more tris than MeshParts. More tris = more lag. If you can upload them to Blender or something similar and make them Meshes that would help. If you can get each wall section to be only 1 mesh it’d be great.
The other thing is the CollisionFidelity. If the walls are large and players aren’t supposed to move through the open spaces you can set the CollisionFidelity to Box or Hull which takes a lot of strain off the physics engine trying to calculate collisions on a ‘rough’ surface made of a bunch of parts, rather than a wall that is just 1 Part.
Moving a lot of Unanchored Parts/Unions/Meshes is going to cause issues due to the strain on Roblox Physics.
How are you moving the walls?
PrismaticConstraints can be used.
They can be moved Using CFrames very efficiently because the walls stay Anchored, but if the player needs to interact with the walls while they are moving it can be an issue.
Many of the explanations of these (and other items that have been posted in this thread by other people) can be found at create.roblox.com