I think something else is going on. Most likely some other part of the calculation is somehow wrong.
The function is "Get ( UUID )" and not UUID. If you place UUID in the Data Viewer it returns an error, field not found. If this isn't happening then there would have to be a field or a Custom Function called UUID. In your case its probably set to use the Get( UUID ) function. That is not a good idea as UUID is a reserved Word. That could also mess up any other use of that function.
I ran into a similar problem a few months back. It took me forever to figure out what was going on, and if I remember correctly, the problem ended up being that I had a FileMaker plug-in installed that supported a similar "UUID" function.
If you have plugins installed, maybe try disabling them one by one, until you find the conflict.
Hope this helps!
I ran into that issue with a custom function that did the same thing.
That was it! Thanks a bunch.