Could you please confirm what happens if you click on the close/"x" button, and try to load the Messages window again by clicking on the Message window at the bottom-right of the Upwork Desktop App?
I'm sorry to hear about the trouble this caused. Could you please try Troubleshooting tips shared in this help article. If the issue persists, please report it following ''How do I report a problem?'' section of previously shared Troubleshooting guide, and our team will assist you directly.