I have had no issues editing BRAW before off of my T5 SSD. I tried editing today off of my internal SSD in my Macbook Pro and the footage in the source monitor will barely playback at all. I can scrub through it fine and plays back in the timeline fine. Just not working in the source monitor when double-clicking a clip. Any solution would be helpful. Also, I shot in 4K DCI 12:1 but have been able to edit 6K Raw from my BMPCC 6K Pro no problem.
You need to add your system specs so people can help you better.
2019 MacPro OS 12.1, 3.2GHz 16 Core, 160GB Mem, 4TB Drive, 8TB Internal Sonnet Raid, Dual Radeon Pro W5700X 16GB LG UF 5k, 27" Tbolt Display, 55" LG C8 Resolve Edit Keyboard, Mini Panel, US 4K Mini Resolve Studio Ver. 17.4.3 Desktop Video 12.1