Why is SSH allowed during rush hour, but not via SFTP?

Question

linux

I can not understand in any way what could be the matter. The bottom line is this:
At rush hour, when the server channel is almost full, I can’t connect to the server via sftp clients (I tried a variety of different OSes). But through the terminal, via ssh, it calmly connects.
CentOS x64
And on another, similar server, such a problem is not observed at high loads.
Has anyone encountered something similar?

Answer 1

And what to look at an error in broad gulls not destiny?

Answer 2

Here the question is what exactly does the server do?
During rush hour (very blurry) maybe someone is occupying the ports your SFTP is using?