HRV graphics

How long have you had the watch? It requires ~19days to learn your HRV values (=baseline) to get the values to compare is the HRV reading in the baseline.

So kind of, not a bug, but the text could tell that you need to wear the watch at least X days in the start, but that would also need probably some new data checks and not really bug that affects anything, just a text would be improved. They have much bigger bugs to fix.

I have the watch almost 2 months,so its a bug. 

Would be kind of crucial information for the original post, as you just talk about "last two nights". 

But for HRV status not working has multiple posts already on this forum and is a known issue, no need to start another post about it.

Here's one: No HRV Status (or Training Readiness for that matter) - Forerunner 955 Series - Running/Multisport - Garmin Forums 

If you don't know exactly how the algorithms work you might not trust them or they might not work/fit for you. Getting the HRV raw value will give indicators that are well known and can give more information like if you haven't changed anything in your training but HRV is changing, you might be getting sick.