I came across a situation where LilyPond crashes caused by a badly placed \pageBreak. I've chopped most of the music out of the example but when I tried to remove more the crash stopped. The error message ends:
Finding the ideal number of pages... Fitting music on 1 page...lilypond: /home/gub/NewGub/gub/target/linux-64/src/lilypond-git.sv.gnu.org--lilypond.git-stable-2.22/lily/page-breaking.cc:1073: void Page_breaking::line_divisions_rec(vsize, const Line_division&, const Line_division&, Page_breaking::Line_division*): Assertion `my_index == 0' failed. Exited with return code 6. 8><8><8><8><8><8><8><8><8><8><8><8><8><8><8><8><8><8>< \version "2.22.1" MI = { r8 e'' g''8. f''16 e''8 d''16 c'' b'4-\trill } MII = { \time 2/4 \pageBreak e''8( f'') g''( f'') | e''( d'') c''-\trill( b'8) | c''( d'') e''( f'') | e''4-\trill d''4 | %5 e''8 c'' g'' e'' | a'' c''' b'' g'' | a''4 fis''-\trill | g''2 | e''8( f'') g''( f'') | %10 e''( d'') c''( b') | c''( d'') e''( f'') | e''4-\trill d''4 | e''8( c'') g''( e'') | a''( b'') c'''( c'') | %15 d''4 b'-\trill | c''2 \break \bar ":..:" e''8( f'') g''( a'') | g''4 c'''8( b'') | c'''( g'') a''( f'') | %20 e''4-\trill d''4 | e''8( d'') c''( b') | c''( d'') e''( d'') | d''4( c''8-\trill) b'8 | a'2-\trill | %25 b'8( c'') d''( e'') | d''( e'') fis''( g'') | b'4 a'-\trill | g'2 | d''8( e'') c''( e'') | %30 e''( f'') d''( f'') } \score {\MI} \score {\MII} 8><8><8><8><8><8><8><8><8><8><8><8><8><8><8><8><8><8>< I think this bug will not be in some earlier version of LilyPond as the file is an old one that at one time compiled ok. Richard