Just tried to use Custom Curves in Resolve 20.0b build 23, and I can no longer gang-link the YRGB curves together (which should be the default behavior) for curve adjustment. In particular, it doesn't work with Editable Splines: only the Y curve is affected. This is something I use all the time, so that's a deal-breaker for me.
Also the master reset for Curves does not function. If I click the Reset All button, the curve does not disappear. If I hit Undo, the curve does not revert to what it was before.

These are pretty catastrophic problems for me and greatly affect the way I work. This is all in Sonoma 14.7.5, MacBook Pro M1 Max (test machine).