Hi Guys,
I appear to have fixed this issue for myself (on WordPress 3.8), the problem seemed to lie in the returned transient data via wordpress not supplying valid JSON.
To remedy this I simply base64_encode() my $tweets before I set_transient(), and base64_decode() before I json_decode().
I have posted my modified inc/get_tweets.php (from v1.4.4) to PasteBin:
https://pastebin.com/4icFpKz5
Good luck!
-Brandon