I have had this issue on 2 iPhones, my previously reliable for 2 years 3GS, (just upgraded to ios5) and my brand new 4S.
Here's what I did on both handsets:
I downloaded ios5 in iTunes, installed [3GS only] then setup as a new phone.
I then went to the Music tab and selected my, 'iPhone' smart playlist which contains all songs above 1-star, (approx 53GB) plus a few more selective playlists and synced successfully.
All worked fine.
Some time later I go back to my main, 'iPhone' playlist and changed the criteria so that iTunes selects 50GB worth of songs by number of plays so I get a bit more space for apps etc, (you only get 54GB of usable space on a 64GB 4S) and sync.
All appears to go ok but when I select a playlist containing say 20 tracks it takes a good 5 seconds to go into the playlist like it is checking/scanning each file then all is ok. If I choose a playlist of say 200 songs it takes longer, maybe 30 seconds to go in then I can shuffle but again this is slow starting to play.
If I go into my main 50GB playlist the 'checking' proceedure, (I am convinced is now the cause of the issue) does not finish before the app launch 'times out' and the home screen appears as the app has crashed and will never launch successfully again.
If I then goto:
Settings / General / About / Diagnostics & Usage / Diagnostic & Usage Data and slide to the bottom I see entries such as, "Music~iphone-2011-11-08-17..." and inside are crash details containing info such as :
exception code: 0x8badf00d
reason: com.apple.mobileipod failed to launch in time
elapsed total cpu time (seconds): 19.928 50% cpu
...there are then hundreds of lines of error codes.
Trying to relaunch the app after double-clicking the home button and closing all running apps or even rebooting the iPhone does not fix the issue as the Music app seems determined to check/verify the contents of the playlist I last went into, my big one!
ONLY WAY TO FIX THIS IS TO GO BACK TO ITUNES AND DE-SELECT 'SYNC MUSIC' THEN PRESS 'SYNC' (REMOVES ALL SONGS) THEN GO BACK AND SELECT 'SYNC MUSIC' CHOOSE MY PLAYLISTS AND LET 7669 SONGS COPY BACK TO THE DEVICE!
My question to Apple is:
Has this bug been spotted, (I am an IT Manager and can recreate the issue) and will the fix be included in ios 5.0.1?