Why are my pushes timing out?

[Thomas Sharpless]

I have a few so-far single user repos on BitBucket.  I have registered an SSH key and push to them using Tortoise Git.  Sometimes this works fine:  I click push, I'm asked for my passphrase, and the commit goes in.  But increasingly often, nothing happens for 2-3 minutes, then I am asked for passphrase, then git reports failure due to closed connection.

I suppose this is likely due to some misconfiguration on my end, but I have no idea what to look for.  Any suggestions?