I've found the answer to this. This had been plaguing me for days, but so happy to have this fixed.
When I go to task manager the process adb.exe was constantly restarting itself. This is what was causing the issue (for me).
Go to Tools -> Android -> Enable ADB entegration. Untick this. Make sure its status appears as unticked. Now go to task manager and killed the process adb.exe, it will not restart itself this time. Now click run, hey presto, ADB runs. Whoop de doo.
与恶龙缠斗过久,自身亦成为恶龙;凝视深渊过久,深渊将回以凝视…