Keepalives can make this sort of problem worse, because they
increase the probability that PuTTY will attempt to send data during
a break in connectivity. (Other types of periodic network activity
-can cause this activity; in particular, SSH-2 re-keys can have
+can cause this behaviour; in particular, SSH-2 re-keys can have
this effect. See \k{config-ssh-kex-rekey}.)
Therefore, you might find that keepalives help