Way to repro:
1. Open Unity and Sign in.
2. Help -> Manage license.
3. Press Return License.
Actual result: From time to time (2/3) window stuck and nothing happens (see screenshot attached). You can close window and continue working with this license.
Expected result: If backend server observes some errors, user should be notified that license was not returned and action was interrupted by timeout, and he can try to return license later.