I found a workaround by exporting the Postman Collection as Collection v1 (deprecated). However, authorization credentials are not imported in this way and you have to manually enter and save them in Soap UI requests.
I've encountered this today and on my end, the issue was fixed by selecting "V1" even if it says "deprecated" at Postman's export page. It seems Postman's v2.1 cannot be processed properly into SoapUI as well. For more details on the steps for fix, you can refer to this page: https://www.soapui.org/docs/postman-collections.html
"an Engineer without a degree, a QA tester without any official certification (just yet ;-) ) "