UPDATE The supposed duplicate is a question on being stucking in \"Waiting For Debugger\" when executing Run, while this
How it worked for me.
1 Start Android Device Monitor from Tools -> Android -> Android Device Monitor
2 Click on Stop for the process you are facing the issue from list of devices.
Android studio 3.0 and Above
Disable the instant Run
I faced this problem in android studio 3.0. Just restarted device solved.
I tried the top three rated answers but failed. After rebooting my mobile, the problem is solved. No more long "Waiting for Debugger".
Restarting Testing device fix the issue for me.