I have noticed one more thing: I am loading into server a lot of counters with create-many.sh.  If there are 600 counters (300 strong and 300 weak), they are loaded normally and shown on the page. If I change to load 800 (400vs400), then in console it shows 0 counters (see attachment). But the REST API returnes all of them.

I have found the number, when the number of counters is > 337*2, then the counters are not loaded by the console. And from the browser's developers tool, I can see that it loads data for each counter, and at once requests to server fails (see screenshot).

Update

The solution for this comes by using a new endpoint (see blocked by linked issue)