I'm not sure if this topic is still active, but I've been having the same problem (as have a ton of people, I guess). I've been trying to get one ringtone onto my iPhone 7 for THREE days now. I was somewhat successful at the end of day 1 as the custom ringtone briefly showed up on my phone, but then I got greedy. I wanted 2 or 3 custom ringtones on there and the iTunes' Gods must have said, "Forget about it!" Upon attempting to sync my 2nd custom ringtone, iTunes DELETED ALL MY RINGTONES!
So, I've tried the following things to attempt to get that single custom ringtone back from my computer onto my iPhone 7 running iOS 11 through iTunes 12.7:
1. dragging and dropping from Windows Explorer to iTunes (both sidebar and the body of "Tones")
2. cutting and pasting from and to the same places as above, using all 3 ways of cutting and pasting
3. uninstalling iTunes 12.7, cold booting, installing iTunes 11, and trying 1 and 2 above
4. uninstalling iTunes 12.7, cold booting, re-installing iTunes 12.7, and trying 1 and 2 above
5. unchecking the box next to Sync Music, clicking the Sync button, then re-checking the box and re-Syncing
There's probably a multitude of other things I've tried, I just can't remember. Suffice it to say I did a Google search on "iTunes 12.7 custom ringtone" and clicked and tried every linked that popped up. I also tried 2 different outside apps: GarageBand and AnyTrans...neither one worked. I use Norton 360 to clean up any issues with quick scans, should they arise.
So, not only did these things not work and not only did iTunes delete my existing custom ringtones from my computer, but the custom ringtones that show up in my Library in iTunes now either have a circle with an exclamation point inside it to the left of the song OR the entire line is grayed out and there's a dotted line circle to the left of the ringtone. Neither will play and neither will let me tell it where on my hard drive the actual .m4r file is located.
I'm pretty much at wit's end. I'm an IT guy, too. I'm having Norton do a Full System Scan right now, which will take a day or so.
Any other ideas?
Doug