Many thanks for the quick reply. I was out of town so apology for my late reply.
I reinstalled the theme and purged Cloudflare cache – voilà! It’s get fine. I don’t understand why but anyway it’s good now.
However, I still have the question why the layout is vertically arranged instead of horizontally. It’ll mke awkward layout sometimes if there are fewer posts under a certain tag. For example, if I only have four posts under a tag (very common case for a new site), the layout is like below (using masonry with 3 columns):
post4 post2 blank
post3 post1 blank
post4 post3 post2
post1 blank blank
I think it could be a bit strange for visitors and they might think the website is (partially) broken.