Already resolved itself, the Nodes counter had the same dip so probably just servers not responding.

Where can I see thos chart?

This is a bug. The crawler don’t finished to get the data for the last time unit and the result is this drop. What some hours and it will be ok.

Looks like a server fault. The Mastodon user count bot sometimes goes buck wild too.

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Where do can we see these graphs?

Just guessing, but maybe this has something to do with instances overload