Android development kit is required to reproduce this issue.
If adb.exe is already running, new instance will not be launched.

Steps to reproduce:
- Kill any instance of running adb.exe
- Open any Unity project
- Enter play mode. Adb.exe will be launched which will launch another adb.exe.
- Close Unity. Navigate to the folder of previously opened project
- Attempt to move the folder. Windows will report that the folder is in use. Process explorer reports Current Directory for adb.exe as the locked folder.
- Kill running adb.exe
- Folder will stop being in use

This can be workaround by launching adb.exe manually in any other location. However, that location will get locked. For example:
- Open cmd.exe
- Navigate to a folder which can be locked
- Run adb.exe with "start-server" parameter
- Attempt to delete the folder. It will be locked.