How to reproduce:
1. Create a new project
2. Build and run as a development build
3. In the Unity editor go to Window > Analysis > Profiler
4. Select the Attach to Player dropdown
5. Enter your local IP address
6. Click Connect
7. Click on the IP address in the dropdown again

Expected result: Nothing happens
Actual result: The connection is closed

Reproducible with: 2018.4.32f1, 2019.4.21f1, 2020.3.1f1, 2021.1.0f1, 2021.2.0a10

Notes:
1. The issue is not reproducible when clicking on other Attach to Player options.