I also just updated to 220.127.116.11 and have a similar problem.
It does not actually inventory the media folder for what is there.Your music may still be there but you nee to rebuild the library file.According to i OS 11.3.1 release notes, i OS 11.3.1 also improves the security of the i Phone and i Pad.You can install the i OS 11.3.1 update wirelessly, but if you’re not getting the OTA update then you can find the direct links to download i OS 11.3.1 firmware (IPSW) files for i Phone, i Pad and i Pod touch so that you can update it manually using i Tunes. i Tunes is the official i Pod managing software, but 3rd parties have created alternatives to work around restrictions in i Tunes. transferring content from an i Pod to a computer is restricted by i Tunes.
software that permits the transferring of media files content between an i Pod and a computer or vice versa.This process occupies both devices, so make sure you choose a time when you won't need to use your current device for several minutes.Learn how to restore your Apple Watch from a backup and pair it with your new i Phone.Usually the files are still there but updating has not successfully rewritten that file and you have to use the old version.If the files themselves are actually missing then that is when you rejoice at having made a backup of your entire computer before ever running any kind of update.I understand why that won't work--but I would lose far more than I would gain. I noticed that in the process my i Tunes library was moved to the Previous i Tunes Library and replaced with a new i Tunes Library approximately 30% smaller. Although I have various backups going back to September 2015 (from Carbonite) they are only 3MB where I expected more like 3GB.