lmchucho, klkitchens, thanks for the replies.
I'm still seeing the jerky movement on both my laptop and my PC. It can be difficult to notice, as it only happens for the first 5-10 seconds. It's most noticable on the platform, and you have to look really closely at the platform. That's why I added white lines, to make it easier to see.
The project I'm working on is meant for mobile, and it is much worse on there (which is why I am concerned)!
I never used to notice it at all on the PC, until recently. So I thought I'd ask the question to see if there's anything I can do to fix it!
If anyone has experienced this themselves, or does know how to fix it, I'd be really grateful for some advice!