YOU SAID:

I don't get it and it's not the first I've seen this

INTO JAPANESE

わからないけど、これを見たのは初めてじゃない

BACK INTO ENGLISH

I don't know, but it's not the first time I've seen this

INTO JAPANESE

わかりませんが、これを見たのは初めてではありません

BACK INTO ENGLISH

I don't know, but it's not the first time I've seen this