Having identical issues with my Prime Z370-A on 0615. Whenever I use manual voltage it just defaults to using the Intel programmed in SVID settings. If I disable SVID then it just sits at 1.1v, which obviously doesn't work for overclocking. Adaptive works, but the actual set voltage doesn't correspond to what I've set in the BIOS. I can get it to change, but I have to keep trying different settings that give me no where near what it's actually set to.
I've tried different combinations of basically every option available in the BIOS, as well as almost every BIOS version that's been released. I've got AC/DC load on 0.001 right now, and with it set to default adaptive completely refuses to do anything but follow the default SVID settings. I'm running at 1.35v with LLC7 on, and I get vdrooping down to about 1.26v on Prime95 small FFT tests. The actual settings in the BIOS are something like 1.3v with an negative 0.5 offset, which somehow lands me at 1.35v. If I change the offset up or down by say 0.01v I'll see completely random changes that don't correspond to what I've actually changed.