Version: 70.something
OS: Chrome

After various combinations of plugging/unplugging USB drives and clicking eject, I got the following exception in the console:
_generated_background_page.html:1 Uncaught (in promise) undefined
Promise.then (async)
importer.DefaultMediaScanner.scanDirectory @ background_scripts.js:7556
importer.ScanManager.getDirectoryScan @ foreground/js/main_scripts.js:33331
importer.ImportController.onScanInvalidated_ @ foreground/js/main_scripts.js:32512
importer.ImportController.onScanEvent_ @ foreground/js/main_scripts.js:32424
(anonymous) @ background_scripts.js:7663
importer.DefaultMediaScanner.notify_ @ background_scripts.js:7660
(anonymous) @ background_scripts.js:7547
importer.DefaultDirectoryWatcher.onWatchedDirectoryModified_ @ background_scripts.js:8107
(anonymous) @ extensions::fileManagerPrivate:236

Once this exception is hit, the Files.app stops detecting new drives. However, chrome is still detecting new drives and mounts them accordingly. If Files.app is closed and the user waits for the background page to stop, re-opening the app will start showing new drives again.