Can't connect via SSH (Network error)?

Question

linux

Hi all!
Faced a problem connecting to a remote server via SSH. The port is not default.
The connection breaks (connection by login and password), although I didn’t change anything in the configs, everything worked:
at first it was:
Network error: Connection refused
then:
Network error: software caused connection abort
In Putty
- in the "Enable TCP_keepalives" option, ticked
- set "Seconds between keepalives" - 5. All in vain.
"Solved" by rebooting the entire server.
Please tell me where to dig.

Answer 1

First: TCP RST or FIN received; second: no TCP ACK received.

Answer 2

Network error: Connection refused

The server was bogged down with requests (frequent reconnects, attempts to log in several times in a row). I fell under fail2ban or just in the limit of connection attempts.