Setting [ITU709(800%)] or [S-Log2] may cause an error in the white balance custom setup. In that case, set the exposure bright first and then perform custom setup.
I guess BRIGHT means oh 5 stops? I'll try that....
Custom WB in Slog doesn't work well. You can try adjusting the exposure (open up), but it's still hit or miss, mostly miss. Switch to another PP. And yes, it's a small pain in the rear. Hopefully they can fix it with a firmware update!
Adjusting exposure doesn't work for me most of the time.
My solution, which sucks but is not the end of the world, is as follows:I have my shooting setting (Flaat, based on slog2) on PP1, then on PP2 I have a profile based on Cine4 but with b/w color; when I want to set custom WB, I switch to PP2, adjust PP, and go back to PP1. PP2 has to be monochrome, otherwise I will often forget to get back to PP1 before shooting.
A measure of how stupid this issue is, is that WB works with b/w color but not with s-log2 gamma.