Can't get iTunes to connect to remote media folder

I have recently moved my iTunes media folder to a NAS, partly because it was becoming too large and partly to use it with another application so can play it on my Apple TV without having to have iTunes running on a Mac.

The folder had been on an old Mac running El Capitan so I started the migration there. All went well for that Mac. I only moved the media folder, everything else in the ~/Music/iTunes folder stayed on the Mac. The local media has been removed and it's all working as expected.

Using the data on the second Mac (running Mojave) is proving to be a challenge. Again, I want to use a local iTunes folder. I have changed the media folder location in Preferences but iTunes is not using it.

The share is mounted and the "iTunes Media" folder is visible in Finder. I can browse to and open any file in the folder without problems.

Each time I open iTunes I check the Advanced settings in Preferences and it is still pointing to the folder on the NAS but not connecting to it (and not giving any errors). If I delete the local media folder (which was empty on this machine anyway) before starting iTunes, it just gets recreated.

Can anyone help me understand why it is not using the location set in Preferences?