Hi Adrian,
My name is Adam, I work with Esri Support, and am working on a open support case @John Gargiulo on this issue.
We suspect this could be a issue with ArcGIS Pro 2.4. Or with the location of the Geodatabase.
Questions:
-What Version of ArcGIS Pro are you using? if 2.4 Have you tried 2.5?
-Can you identify the full path to the Geodatabase? is that drive local to the computer or on a server?
We appreciate your input, it will help the investigation.
Cheers,
-Adam