targeting one country tanked my performance

So I created a new campaign and targeted the whole world but noticed that i was spreading my budget too thin and there was 0 conversion but i was getting a lot of clicks and impressions then i decided to target only two countries and then my performance tanked i got only 1 click and 16 impressions and nothing else and i'm sure if i revert this targeting my campaign will continue to work normally and what i noticed when targeting both these countries my AD doesn't show either due to low ad rank which i don't know how to fix because every description of it out there is too vague. I guess its an intentional thing done by google but really i don't know why my ad isn't showing up in both these countries but when i target the whole world my campaign continue to run normally.

Update: i'm using maximum conversion but i think i figured the issue, when i changed the target location, i also changed the target cpa to $29 but when i view the insights tab i see google is using the target cpa learned from historical data which was $4 which is low and it can't compete with new targeting so now the question is there a way to reset this?