I’ve been using Audacity for years on a desktop iMac running OSX 10.6.8, with no difficulties at all until very recently. Current version of Audacity is 2.1.2.0.
After I’ve edited a music file of any length and transferred it back to iTunes, or emailed it as an mp3, when I play it back, it will only play between 44-46 seconds of the track - even though the track is much longer than that - and then skips to the next one. Help!
I think Google has solved this for me; it seems to be an iTunes import issue and not related to Audacity, and apparently many others have experienced this issue. The fix involves importing the files into iTunes by dragging and dropping them into the “Automatically Add to iTunes” folder. When I get them into iTunes that way, they play normally with no skipping. Very strange indeed, but happy to have found a solution! 
Thanks for posting your solution.
I’ve not experienced this problem myself, but from what I’ve read on-line it seems to be a problem with iTunes’ library database. Some iTunes users have reported that when there’s a lot of files affected, they’ve fixed it by deleting the entire library (“keeping” the “files”), and then starting over adding their files to the library. Anyone taking that approach should be very careful that they don’t accidentally delete the files.