Bottles are erupting !

I've never mixed the sugar into my beer and it hasn't been a problem. I do let the auto siphon tube wrap around the bottom. Of the bottling bucket so it makes a little whirlpool affect. I've always had consistent carbonation

 

The three bottles didn't gush, but did they have any carbonation?

There have been inconsistent reports on the success of using the auto-siphon in the bottom, so I think it also becomes a question of how thick or thin that sugar solution is. A syrup in one cup of water may be too thick to disperse with just the flow of beer around it. Gentle stirring at the beginning and 2-3 times during bottling is the only way to be sure you keep that sugar in suspension. I usually boil my sugar in about a quart of water, and I still use stirring to make sure it's mixed well.

 

Check the neck for rings. How much sediment are you transferring? CO2 likes to hide in sediment, and if you're not allowing a good slow chill to happen before opening it when you have a cake on the bottom. They will freak out for freedom when you crack the bottle open.
Also, stir your priming sugars in. Don't just plop the liquid onto the bottom and expect the hard work to happen when racking over. Without additional motion like activity. Liquids will tend to sit, and happily so. You probably have hot spots, and some sediment issues in your bottles.