How to resume normal iPhone volume after notification causes volume to get stuck in lower volume mode?
Yes, I too have had this problem many times. (I have been told it is a known bug in iOS having to do with playing MP3 files that are shorter than two second.) The easiest way to get your phone back to normal volume is to pause the music (or audio/video, as the case may be) and then resume it. The volume should be back to normal after that.