The page at https://bn.wikisource.org/s/ufz looks like the screenshot at https://bn.wikisource.org/s/acge in browser-chrome, device Redmi 1S smartphone, OS Kitkat. There are three stanzas in this poem; lines in the first two stanzas are preceded by multiple colons. The middle stanza has no colon and has an apparent larger font-size in mobile browser. The problem resolves by adding a single colon before each line of the first and the last stanzas. The problem appears on android browser but in desktop-emulation-of-mobile-mode at https://bn.m.wikisource.org/w/index.php?title=আবোল_তাবোল/আহ্লাদী&mobileaction=toggle_view_mobile the problem is not shown. See https://bn.wikisource.org/s/abwn for discussion.
Tentative assignments to each of MediaWiki-extensions-Poem and Mobile-Content-Service. Please review and correct as appropriate.
There are two distinct aspects to this fault: the display issue on the android device; and the inability to emulate (and thus debug) same in desktop-as-mobile-mode.