1. While the xbox is powered on, perform a hard reset on the console by pressing and holding the power button on the front of the console for 10 seconds until it turns off and turns back on again. Then proceed by deleting your profile in the profile settings (I'm not talking about the test account section).
2. Re-add your same profile and navigate in the settings to find the factory reset option and do it and if you are able to please delete all content on internal SSD when asked, if you are unable to due to data not being backed up, you still need to factory reset your xbox however choose the option to keep all your files. Then once it is reset, reinstall retroarch along with it's dependencies and open it (Make sure your USB storage device with your games is unplugged from your xbox).
3. Open retroarch and update everything in the online updater such as core info files, assets, everything like usual. Then navigate to "load content" and go to the bottom and into the settings and enable the option to show hidden files. Then go back into the directory list and plug in your USB storage device directly into a USB port on the xbox not a USB hub (I don't know if it matters, although I am using my USB storage device through a powered USB 3.0 hub after I fixed this issue for myself). Now go back 1 screen and re-enter the directory list and you will see your E: directory and now hopefully it should show all your contents that you have on it now and you can start importing manually like usual off of your USB storage device.
NOTE: if you are still having the issue of no contents appearing in your USB storage device in the E: directory in retroarch upon following this tutorial
, then try to install retroarch 1.9.10 and then run it and follow step 3 again and hopefully it should work and you can now uninstall the 1.9.10 version of retroarch and download and install the latest version from the retroarch website.
NOTE: if you are always getting a black screen upon booting any game just reset your retroarch configuration file back to default settings and close retroarch and open it again and redo everything unless you have backed everything up first and all should be well.