Closing. Fixed by this commit:

commit 4b06250ef1fe98a766938862912383d2ee051dfb
 Author: Juanma Barranquero <lekktu@gmail.com>
 Date:   2019-10-09 12:36:57 +0200

     Do not use tick faces beyond ZV (bug#37641)

     * src/xdisp.c (maybe_produce_line_number): Check beyond_zv
     before using a tick face for the line number.  Move all face
     selection code outside the loop that draws the line number.