I'm using iTunes 12.7 and iOS 11.3. A while ago I added a long list of custom ringtones that are still in my phone. iTunes can't see them (Tones section is blank). I can use iExplorer to delete the files from iTunes_control, and they then disappear off the phone, but the iExplorer media library still shows them there.
At the same time, I can't transfer any new ringtones to the phone. When I try through iTunes, the files remain greyed out and never transfer to the phone. When I try through iExplorer, the files transfer but never appear on the phone.