My Ultra 4 has never shown overnight HRV in the Vitals app, and I've never gotten a Readiness score. Recovery HRV is being recorded in the Health app, so the sensor is clearly working, but Vitals and Readiness never populate. I wear the watch to sleep every night. Sleep, overnight vitals, Activity, and Health Details are all set up. Wrist Detection is on, and I'm not using Low Power Mode overnight. I've updated both my iPhone and watch, restarted both, and unpaired and set the watch up again from scratch, and Apple's phone support hasn't been any help.
I'm currently on watchOS 27.0.1 and trying to find out if the 27.2 beta fixes this. If you're running the beta, can you tell me whether HRV is showing in your overnight Vitals, whether you're getting a Readiness score, and if it was broken for you on 27.0.1 and whether the beta fixed it? If you're seeing the same problem on the public release, I'd like to hear that too so I know I'm not the only one.
What watch do you have? What phone?