Web Core Vitals for mobile sudden drop

Hi Vadim 

We have a niche site that only gets a relatively few hits and, as such, there never is any live CWV data to look at.  I don't know how many users are necessary for results.

In general, this data is aggregated from users who have opted-in to syncing their browsing history, have not set up a Sync passphrase, and have usage statistic reporting enabled.  It's captured on a rolling 28 day cycle.  

It may be (if there is merit in my suggestion), that you may see data once more, when there is enough, for it to again be meaningful.

I checked Analytics and I don't see any issues with the traffic or reporting

This isn't about any reduction in traffic necessarily, it's about how much of that traffic, actually have the relevant things enabled, in order for Google to perform meaningful live CWV calculations. These tests are based on certain 'opt in' user criteria.

As I said above, for Google to capture the data, users have to have opted-in to syncing their browsing history, have not set up a Sync passphrase, and have usage statistic reporting enabled

So if say 1,000 visitors last month met the criteria (N.B. I've no knowledge of the numbers required!) and this month it's only 50, clearly the visitor numbers could be identical, but the available data would be much less pro rata.  When there isn't enough, Google certainly doesn't show it.

Your own data shows that the majority of users are new.  So... if less of them are allowing Google to capture their live browsing habits, then you Google might not get the prerequisite amount of data to aggregate and therefore can't show you it.