Laggy playback, delay on start/stop

Hi there,

So I'm editing a vaguely long-form project (around 48min RT) with 4 tracks of cameras, 3 tracks of mono audio. Minimal effects (some dissolves, a basic LUT applied with Lumetri).

The footage is a mix of three FS7s shooting 1080 25p S-LOG3 AVCI 100 in an MXF wrapper and one DJI drone shooting some 4K h.264, although these are used very sparingly throughout the edit and are therefore rarely under the playhead in any track stack.

Nothing about this timeline to me seems to be something I'd expect Premiere to struggle with, yet even using the lowest-res option ProRes proxies i get terrible playback stuttering and huge lag between start/stop playback. I'll hit spacebar and it's around 5-10 seconds before anything happens.

This is also the case when navigating around the timeline. I'll click the playhead somewhere new and it'll be 5-10 seconds before my Program picture updates.

Neither proxies being active, nor playing at different playback resolutions seems to have a significant impact on this.

Media and project are on a fast drive separate from the system drive and I've got CUDA acceleration enabled. Scratch disks are on a fast SSD.

My computer should be more than up to this task.

System specs (temps are with premiere playing back):

Operating System

Windows 10 Pro 64-bit

CPU

Intel Core i7 6800K @ 3.40GHz 28 °C

Broadwell-E/EP 14nm Technology

RAM

64.0GB Unknown @ 1197MHz (17-17-17-39)

Motherboard

Alienware 09G12C (SOCKET 0)

Graphics

DELL S2817Q (3840x2160@60Hz)

DELL S2817Q (3840x2160@60Hz)

3071MB NVIDIA GeForce GTX 1080 Ti (Dell) 32 °C

Storage

476GB SK hynix SC308 SATA 512GB (SSD) 30 °C

3726GB Seagate ST4000DM005-2DP166 (SATA) 32 °C

447GB SanDisk SDSSDHII480G (SSD) 34 °C

Optical Drives

HL-DT-ST DVD+-RW GS40N

Audio

Sound Blaster Recon3Di

The only thing that's potentially an anomaly here is the project was initially created on a Macbook Pro and I'm now editing on a proper workstation. I tried consolidating it to a new project file to see if the .prproj was corrupt. No effect.

Any help would be massively appreciated.

Best,

Archie