Looks like BitMex spun up a little Bitcoin node client tracker:
There is also Luke Dashjr's node client tracker
As well as the one run by BitNodes
And there is Coin Dance's node tracker
And something called Bitref (which I had never heard of before)
And Clark Moody's dashboard exposes a little info about node clients as well
There is also https://knotsgoup.vercel.app/ which uses the Bitnodes API.
Thanks! There used to only be a few of these, but now there are quite a few, hopefully mostly using their own data sources.
BitMex's tracker is obviously immature; they report below 500 nodes, while CoinDance reports over 23k.
I like that they publish their view for transparency, although anyone interested in this information must realise that obtaining an objective view of the entire network is practically impossible.
They don't monitor the entire network, they only count the peers that are currently connected to their nodes.
I quoted that same line in another comment...
This bitmex tool is somehow not getting the correct data...
I don't think anyone can produce perfect or authoritative data for this sort of problem. Some nodes don't listen publicly, and can only be found by running enough listening nodes to saturate the network. If BitMex's tracker is new, then they might still be undergoing fluctuations that make their data unreliable.