How can I interpret the given stats please? It is clear that the first node is syncing OK. The second is down—I can see this also in logs. But what about the other two? They're only sending but not receiving.
Is that normal?
It's just the opposite. Your node is sending to these nodes but not receiving anything from them.
Either these nodes have not added your as a neighbor, or you are the only neighbor for them who provides new transactions (in other words, you are the only link of them to the live tangle), meaning that you are "feeding" these nodes with all your transactions but never getting anything back.
In any case, talking to the node operators and
might be helpful.
I found the reason of this outlining behaviour.
It was an indication of the issue in communication. Basically my VPS was dropping UDP packets due to their MTU1650 and so it was sending and not receiving anything back.
So for those having the same issue. Try to switch completely to TCP.