less in -current is terminally broken when handling long lines.
The problem is demostrated on the video:
First, more is called, it correctly scrolls the file from top to bottom.
Less, though, displays `END' right away like the file is shorter than terminal height and does not let scroll at all. It only displays 5 last lines of the file and a part of previous line.
The problem may also be reproduced when scrolling through `pstree` output with a long of long commands running. less will skip lines and eat away long ones.
IMO that's a blocker for 11.0-RELEASE.
That's reproducible in FreeBSD 11.0-CURRENT #0 r295763, but was an issue in current for some time.