I know it sounds weird, but it actually happens on my end.
I copied one overleaf project (created several month before) to a new one, so the content should be exactly same.
I compiled those two documents, it returned with pdf with slight variations.
For the old project, this is the end of first line and second line of title,
For the newly copied project, word "communities" went to the second line.
For other parts, this situation happens a few times.
What might be the cause? I diff-check all tex files and format files in those two projects, and it is exactly the same.