I have the same problem and I believe is something related to the code and the hosting (namecheap). When I try to search a product to be imported the loading gif stays and I’m getting the following error on the JS console.
columnNumber: 1831
?
fileName: "https://mydomain.xyz/wp-admin/load-scripts.php?c=0&load%5B%5D=jquery-core,jquery-migrate,utils&ver=5.2.1"
?
lineNumber: 2
?
message: "search_callback was not called"
?
stack: "error@https://mydomain.xyz/wp-admin/load-scripts.php?c=0&load%5B%5D=jquery-core,jquery-migrate,utils&ver=5.2.1:2:1831\nb.converters[\"script json\"]@https://mydomain.xyz/wp-admin/load-scripts.php?c=0&load%5B%5D=jquery-core,jquery-migrate,utils&ver=5.2.1:4:28536\nWb@https://mydomain.xyz/wp-admin/load-scripts.php?c=0&load%5B%5D=jquery-core,jquery-migrate,utils&ver=5.2.1:4:18814\nx@https://mydomain.xyz/wp-admin/load-scripts.php?c=0&load%5B%5D=jquery-core,jquery-migrate,utils&ver=5.2.1:4:22259\nsend/b.onreadystatechange@https://mydomain.xyz/wp-admin/load-scripts.php?c=0&load%5B%5D=jquery-core,jquery-migrate,utils&ver=5.2.1:4:27819\n"
