Whenever I am trying to open the console directly or go to Inspect mode from Lightning Experience, Salesforce switches to Classic and then I am not able to debug. I keep refreshing and then it sometimes works again. Okay so is that bug or am I doing something wrong because it is pretty annoying..? I am currently using a Developer Edition org. I have never seen anything similar happening to any of the sandboxes I have been working on before.
As per this thread, This will usually happen when your "Toggle Device Toolbar" is turned on, and the reason being lightning experience not available on mobile browsers. If your device toolbar is switched on, means you're on the mobile browser mode and hence you go back to classic. Turn the toggle off and then try debugging in web inspector and it should work fine.
More reference here