This is the 3539th most frequent Korean word.
문제들이
"Problems" or "issues" (plural form).
Here, '문제들이' refers to various issues occurring at schools in a general sense. It is the subject of the sentence.
요즘 학교에서 발생하는 문제들이 심각해졌습니다.
The problems occurring in schools these days have become serious.
In this usage, '문제들이' specifies the difficulties encountered during the project.
우리 프로젝트에서 문제들이 생겨서 일정이 늦춰졌어요.
Problems arose in our project, causing delays in the schedule.
Here, '문제들이' stands for the challenges or obstacles that are expected to be addressed by the proposed solution.