Ive been seeing this a lot but for some reason client memory on the phone is a LOT higher than client memory on PC. Shouldnt memory usage be the same across devices? If this is a normal thing i would love to know why this happens 
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Ive also noticed that the client memory increases and decreases a lot on devices (Sometimes going from 500 to 1000 and back down to 500) Eventhough there arent any instances being created/destroyed.
Client memory depends on the RAM your device has. Most new mobile phones have 4-8 GB RAM, but low-end laptops (which most players use in my experiences) usually has 4 GB.
The client memory also depends on other tasks running on your device. If for example another game like GTA or Photoshop is running on your pc, there is less memory available for Roblox. This is why it fluctuate, even when nothing changes in your game!
I hope my answers are right and understandable!
Here’s a shot in the dark. A reason that may effect memory usage on different devices isn’t really how you made your game but how it runs on these devices. Roblox on mobile isn’t the same as on PC. Even the Roblox app on iOS and Android would be different since they are two different operating systems. This means that the implementation of each of these apps and software may be different and allocate things differently. Even the operating systems could allocate slightly differently. This is all hidden from the Roblox game developer since it has been abstracted away that allows you to make your game easily without thinking about what’s underneath. I would say that the differences could come from that and how Roblox works on different devices. Different hardware and different operating systems could definitely effect this.
This is just a shot in the dark from a computer science major in university.
The weird thing is i’ve seen other games which look like it should be much more client memory consuming run fine on my phone. Thanks for the good reply btw 