Why is my kindle doing this?

[SandStorm]

My kindle has stopped automatically syncing to my recent purchases. I've had to go onto my amazon account and tell it to download my new books. I've got a good internet connection and it's only just started doing this. I haven't changed anything recently on my settings or passwords.

What do I do?

I experienced the same situation.
I went to my account and downloaded those books (all of your Kindle purchases are listed there). I installed Kindle on my Mac and my phone in the last week so I can use them alternatively.
I bought 2 books since and they were downloaded so I don't really know what's going on.

Mine used to do this sometimes. I had to turn it off completely, turn off the wifi, count to 10 and turn them both back on.

Failing that Amazon customer services are very good