Final answer:
The most critical issue with the introductory paragraph is the lack of unity under a single thesis, which undermines the coherence and effectiveness of the entire essay.
Step-by-step explanation:
The single most important problem to address in an introductory paragraph during global revision is most likely the lack of unity under a single thesis. The introduction is meant to establish the problem and provide background information that sets the stage for the entire essay. A failure in this aspect impacts the overall coherence and ability to effectively engage with the reader on the chosen topic. Since most paragraphs lack unity under a single thesis and major questions from the assignment instructions are unanswered or are addressed with little attention, it is critical to ensure the introduction aligns with the paper's thesis to maintain focus and provide clear guidance for the paper's content.