I thought of another thing. If it's still overly dark, even with the new preset, it's possible my custom LUT isn't being loaded in the second lumetri filter, so check on that. I believe this SHOULD be embedded into the preset, but if it's not, then I can upload that separately.
Basically what the preset does, is first it compresses the 0-10,000 nit HDR range into the 0-100nit SDR range, and then the second filter performs a transformation from rec709 gamma/color into smpte2084 gamma and rec2020 color. So without the second step, you basically get an image that's 1% the brightness of the original. Open up the second Lunetri effect and see if the LUT is active. Try checking the active checkbox above the LUT selection drop down. If checking that box does nothing, then the LUT is not embedded correctly and needs to be uploaded separately.