I also just watched your video: you had it set to medium scalability, and lumen just flat-out won’t run on medium. High is the minimum, and that’s mainly targeting open-worlds. Epic settings is what it takes to get genuinely high-quality GI.
Furthermore, your trees don’t appear to be nanite. While I couldn’t speak to their construction, lumen and nanite are pretty much joined at the hip as far as performance is concerned. Nanite allows for the fast construction of the surface cache, and without it I wouldn’t be suprised that lumen is behaving poorly.