When I apply a linear gradient to a shape and try to adjust it, both handles jump out from under my cursor as soon as I drag them ~120 px to the right making it difficult to accurately adjust the gradient.
Sorry to hear you are having trouble using linear gradient to a shape in XD. Would you mind sharing the OS and XD version of your machine? A screenshot or video of the workflow will be helpful for better understanding. Is it happening with every file or with a specific file?