Can't come up with anything on the spot. But sometimes I see text I wrote and think why I put "a" or "the" instead of vice versa. Sometimes it's just not clear enough wether this item is specific enough or not.

On the other hand, I omit article completely more frequently than using a wrong one. I find I have to consciously think if I should use an article and which article should I use. When I write/talk quickly without double checking, shit happens. Even after using English a lot for 2 decades, articles is just a foreign feature that I have to use consciously.