hey man. I've been working with poweramp for years (and it currently runs on my tablet), but i have to be honest with you on this one... the MIUI app is (except for it's theming) exacly the same and has a better lockscreen widget (in default lockscreen). it's hard to trow poweramp away, but you might need to consider it.
okay. some sollutions:
- clear the app cache and app data of poweramp trough [applications settings] in the android settings app
- clear the app cache and app data of the default music app (they import eachothers musicdata)
- clear the app media-**** apps. they contain album art data, duration data, thumbs, etc. stored to sdcard>android>media.com.something
- get rid of some apps. yes. playing big mp3 files or flac audio costs the phone an amount of data
if none of the above work try this:
1 uninstall both poweramp and poweramp unlocker
2 go to your sd card and remove everything poweramp related in android folder and poweramp folder..
3 (advice) go to your music folders and remove the "albumart.pwm" files those are the albumart and music data files"
4 install poweramp after a fresh reboot
5 install the unlocker
if none of the above work.. concider the stock app or living with it.
other thingy.. not confirmed... the stock music app stores media data and playlists. the music app coming with MIUI is not googles stock app. it could be that poweramp is conflicting with a missing app (since you have the "library mode" and music data including id3 taggs get stored in both the files and the stock app).