In Japan, eggs had been considered the epitome of price stability and were often referred to as an A-student in terms of pricing in the market.
こんにちは！
ご質問ありがとうございます。
ご質問について、いくつか言い方が考えられますが、例えば、
In Japan, eggs had been considered the epitome of price stability and were often referred to as an A-student in terms of pricing in the market. However, recently, that is no longer the case.
とすると、『日本では、卵は小売価格がほとんど変わらない典型的な例とされ、物価の優等生と言われてきました。でも最近はそうでもなくなってきました。』と言えます。
役に立ちそうな単語とフレーズ
A-student 優等生
no longer もはや～でない
参考になれば幸いです。
In Japan, eggs have been considered key in demonstrating pricing stability since their retail price hardly ever change. Unfortunately, recently that is no longer the case.
ご質問ありがとうございます。
「日本では卵は小売価格がほとんど変わらず[物価](https://eikaiwa.dmm.com/uknow/questions/48217/)の優等生と言われてきました。
でも最近はそうでもなくなってきました。」は英語で「In Japan, eggs have been considered key in demonstrating pricing stability since their retail price hardly ever change. Unfortunately, recently that is no longer the case.」になります。
ご参考になれば幸いです。
日本 
アメリカ合衆国 
