I'm not familiar with Garageband. I suggest you transfer a known good file from the iPad back to your computer via iTunes. See if there is any obvious difference with the file, compared to the ones that will not go the other way. I would expect a filename suffix that is not required on your computer, may be required by the iPad's Garageband. It could be as simple as adding the correct suffix.
Early on in older version of the iOS, I have issues with file sharing and the Pages app. It has long since been corrected for me.
Going through the steps that I use for Pages ......
Connect the iPad to the Mac
Click on the apps tab in iTunes.
Go the the Files Sharing app list and click on GarageBand.
Drag the file from the Mac to the file sharing window in iTunes.
Open GarageBand on the iPad.
Tap on the + sign
Tap on Copy from iTunes.
It must be similar in GarageBand I would assume. Is that the procedure that you are using?
I've tried that. Everything works until the last step. When I click on iTunes it doesn't offer me anything to open/import. It tells me there are no files available. In my iTunes shared account I can see the file as being shared. The problem lies within the iPad version of Garageband. It won't recongnize the Garageband file from my iMac. This is more than a bit perplexing. One would think the same program would at least be able to open a file at the very least. I can understand if there's an issue with some of the features being modified in a simpler version but I should at least be able to open and play the file, right?
I would think that you should be able to open and play the files on the iPad, .... unless if there is a compatibility issue. Are you running the latest version of GaragBand on the Mac? I don't use GarageBand at all. I have opened it on my Macs over the years and fiddled with it, but I really know nothing about it.
Have you seen this support site?
I did double check to make sure everything was updated. I've got the latest and greatest on all the apps on my iMac and iPad. The only solution I've seen offered is one that involves changing the coding when trying to transfer the file. This seems a bit odd for Mac products. I do not want to have to go into every single garageband file and change the coding to be able to transfer it to my iPad. Weird that this would be the only way to make it work.
I'll dig more into that support site Demo. Thanks.