There is definitely an issue with DataSources albeit just for my composite projects. Steps I have taken so far:
1. Opened the 5.0.0 workspace in 5.1.0
2. Clicked OK to update the Composite projects.
3. Opened a testcase in the ValidationService-soapui-project_new project with an excel DataSource and confirmed the path to the excel spreadsheet was still correct: "${projectDir}/ValidationService-soapui-project/TestSuiteValidationService/DataSource/DataSource-ValidationService.xls"
4. Attempted to run the DataSource to return 10 rows but no rows returned.
5. Attempted to run the testcase and received the following message for the DataSource Test step "Missing property values in DataSource Row"
6. I then changed the path to be an absolute path and attempted steps 4 and 5 again but again nothing is returned
I then created a brand new workspace with a new composite project referencing the same validation service and having a DataSource step pointing to the same excel spreadsheet in SoapUI 5.0.0 then opened it in 5.1.0 and it worked with no issues.
So clearly there is something about my composite projects that are causing issues.
Edit: I've figured it out! Excel Data Sources with 35 or more properties stops working!