Yes, I fixed the 'Unleash Gargantuar' bug for the lost city...
There is actually 2 bugs with that one.
The first (on all devices), is when you run into him (and even kill him) on the first level he appears, you can't get the achievement then. Big misleading wording by EA (again). It's on the second level ONLY that he appears that you finally can get the award.
That's the first bug..
The second bug, is there is a glitch that doesn't register the achievement even when you run into him on the second level he appears in when in The Lost World.
In order to fix it, I had to replay a number of the worlds he appears in, AND scroll down your achievement list. While scrolling, tap on the little icon where his FACE is supposed to appear (the spots that update with an image when you unlock them). Then suddenly the icon appeared and stayed there. LOL.
As for the Time Traveler, that one is bugged too. I've done just about every possible combination on iOS, and it STILL never works. So don't bother.
One thing you will find out here, if there is a bug where you get a few extra gems than you're supposed to, keep it to yourself. The second EA finds out about anything like that, they'll fix it SO FAST your head will spin. But anything else that doesn't directly affect their pocket, you can expect to wait years, if ever.