iPhone won't play music file attachments from email anymore

hello all....I play in a band....we record our jams when we practice....I send the jams to my bandmates via gmail by attaching the files....for some reason all of a sudden, my bandmates and I cannot play those music file attachments from the email on the iPhone anymore....it loads like it is going to play and then a play button with a line through it comes up and won't play......why did this randomly happen? and how do I fix this? never had this problem happen before and i haven't changed the way I've been doing this