Timeline Playback issue on client Mac Book Pro - DR 17

Hello. I've setup a Resolve environment for a client's MacBook Pro. Version is 17.0.39.
The client is pre-editing with only the 1080p 24 prores422 proxies of the original footage (not original footage+linked proxies) on a 1080p 24 timeline.
Proxies, cache, projects and optimized media is on an External USB3.0 5400rpm HDD.
Proxy use and optimized media are unchecked as I am speaking.
GPU is set to Metal on the client's MacBook Pro.
This MacBook Pro is underpowered on the GPU side (i7, 16GB RAM, Nvidia 650M 1GB, Intel Graphics 4000 1500MB) but the very same setup (Metal) with external HDD has no playback issues on an older MacBook Air used for quick metadata managing with an even lower grade GPU. Same prores422 proxies.
I have the same setup on my workstation but with the original footage + linked proxies generated by Resolve and having no issue either even without EGPU.
What could be the cause?
Thank you

Which GPU is activated in the prefs?

Which GPU is activated in the prefs?

Hello. We solved the problem by deselecting "auto" in GPU selection and then selected both GPUs (display and discrete). Then switched from "Metal" to "auto". It now playbacks at 24fps together with quarter resolution (on proxy files!).

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