footage lagging even after rendering entire timeline

I have a project file sent to me by someone else, where for whatever reason the footage plays completely fine on their PC but is unbearably laggy on mine.

things I've tried:

- creating a new sequence in the same project file with different footage plays fine

- using proxies does not boost performance at all

- rendering the entire timeline has no effect on performance

- computer is more than capable of editing this type of footage and has done so many times before

- Clearing media cache has no effect

- Working with small sections of the footage in a smaller sequence helps, but it is still unusable

- Rendering audio doesn't help but also doesn't seem to work correctly. The rendering window appears for a split second before disappearing.

- global fx switch has no effect on performance.

- updating  Premiere Pro did not help, tried v 23.0 and returned to 22.6.2

- using Multicam instead of stacked footage does not help

PC specs:

RTX 3070 TI

AMD Ryzen 9 5900x

64GB ram

Screenshot of the rendered timeline in a smaller sequence

I am currently re-encoding all of the original media in hopes that might help, but given that rendering the timeline and using proxies made no difference, I'm not confident it will.