In the two different scripts (Uthmani and Indo-Pak) the juzu stops sometimes differ, for example 4th juzu starts from "lan tanaalu al-birr" in the indo-pak, while that is the start of the page in the Uthmani script, but the start of the juzu is the next ayah "kulu at-ta'aami" as indicated on the side of the mushaf which also indicates the hizb in the Uthmani script. This also is the same for other juzu, such as 7th juzu, and so on.
Wa alaikum assalaam wa rahmatullahi wa barakaatuh
The division of the Qur'an into specific 30 juz' marks was not part of the revelation and done later. Therefore there are slight differences in some copies as to where a juz' begins and the one before it ends. The division into ajzaa is not part of the Uthmani script. A benefit of juz' divisions is to divide the Qu'ran into 30 parts so one can read a juz' per day and complete the Qur'an in a month's time.
Please see the following previous answered question on the division of the Qur'an into specific ajzaa'.