More like a question. LoadUI and Load Tests

I attempted to run a LoadTest based on a SoapUI project however while single HTTP REST requests work fine in SoapUI in both LoadUI and SoapUI when i attempt multiple (a number of VUs or a number of Requests in LoadUI), my REST API backend code does not execute as it does for a single request.

Are there any limitation to SoapUI and LoadUI when executing multiple requests/VUs? Has anyone else encountered this problems?

I use the GUI test runner for SoapUI if it matters.

Thanks in advance!