Ran into this after Chrome had updated to version 80, but after that I was unable to debug my app running in the simulator by navigating to localhost:9090.
Apparently, there is a workaround: instead you should go to chrome://inspect/#devices, click the "Configure" button next to the "Discover network targets" checkbox (which should be checked), ensure that "localhost:9090" is in the list inside the dialog which opens after you click the Configure button, and close the dialog with the "Done" button. After the simulator has been opened, it might take 4-5 seconds for the URL to it to appear below the "Remote target" in the inspect/#devices tab.
dabs This problem is also in 7.x, but we are currently working on the solution. In new beta 7.x this fix will be available (we found the way to fix this, but integration and rebuild will take a few days). What operation system are you using?