Hello,
@kostajh asked me today why a horizontal line appears in Czech Wikipedia:
When I looked into that, I noticed that this bug is new-vector specific. It does not happen in the old vector. I also noticed that this bug disappears after scrolling/mouse moving when safemode is disabled (ie. the default), but is apparently permanent with safemode=1.
See screencast at https://commons.wikimedia.org/wiki/File:Bug_report_-_Horizontal_lines_appearing_in_new_vector_at_Czech_Wikipedia_-_20210226.webm.