Here are some brutal ones:
"Fanny" and "Irma La Douce" tossed out all the songs and used them as background music in non-musical films.
"The Gay Divorcee" (on film with Fred & Ginger) cut ALL the songs except "Night and Day," and they even changed its title from "The Gay Divorce" (too harsh a title for 1930's audiences).
But since you used the word "suffered" there are worse crimes than these. Some films have been successful and faithful to the intent of the original shows, despite major changes in the score (like "Cabaret" and "On the Town").
Here are a few that truly "suffered" with fatally bad decisions...
"Annie" --- because they cut several songs and replaced them with FAR WORSE ones, and because they cut the MAIN SONG IN THE SHOW "Tomorrow" and replaced it with "Dumb Dog." Annie only sings the reprise of Tomorrow in the White House. This basically killed the entire heart and message of the show. A truly idiotic move.
"Phantom"--- because every song and especially the recitative sections are painfully under-tempo, to the point of exasperation and ultimately disinterest... curiously, until you get to Masquerade, which is sped-up to the point of lunacy, as if we're watching and hearing it at the wrong speed. The musical director killed this film with his baffling tempos single-handedly, and Webber should have known better when they were in the pre-recording sessions. I've tried to watch the film a couple of times recently and I just... can't... get... through... the... slow... tempos. zzzzzzzzzzzzzzzzzzz
"Jaws is the Citizen Kane of movies."
blocked: logan2, Diamonds3, Hamilton22