All this time, only once I have edited my feed setting and as far as I know it has no problem. The problem appears when I tried to validate my feed to Feed Validator.
The method I have tried is transferring my feed to FeedPress and at the same time, I heard a rumor that FeedBurner will closed soon. I will not talk more about this rumor and I definitely stay in FeedBurner until it is completely closed. Howsoever, as the saying goes "take an umbrella before it rain". Back to the topic, the method is useless.
Ok, now I'm going to explain, this problem is not because of the template or from the feed setting, but the problem from blogger sites. The 'georss' is the location tag inside post, which it also serves as geo targeting.
The trick is, go to Posts like you see in the picture below, and set the element numbers to 25.
Only 25 articles that is listed in the element need to have empty location tag. After 26, you can insert the location tag. I mean, let say if you have 25 articles and you create again. Your article will be 26. So, you can insert the location tag.
Try to validate your feed on W3C or Feed Validator, you can see the word "Congratulations! This is a valid Atom 1.0 feed."
This trick only can be used before the blogger.com fix the problem. Anyway, if you have any problems please feel free to give comments and we can solve it together. :)