Hey! I've seen that many people seem to get the "L-104 (video_session_registered)" error or having shadow get stuck at the "shadow is ready" loading screen, something I've had issues with a lot too.
I've found a way that so far has worked every time for me, here are the steps:
• Force shut down Shadow from the app (hit the question mark icon and then the red power icon and wait till it says "shadow is off"
• Close the Shadow app.
• Now open a browser on any device and go to the shadow website and select "Launch Shadow PC in Browser"
• Click "Start now", log into your account on the shadow pc and wait for Windows to be fully booted.
• !! Leave the browser open
• Now start the shadow app and it should start without an error, once it has connected and you're at the desktop of your shadow pc you can close the browser.
• *I've sometimes had the cursor be invisible after but that's easily fixable by just restarting streaming (open the shadow overlay and click the circular arrow icon or use the ctrl/cmd+alt+R keyboard shortcut)
I can record a video with all the steps if anyone wants that, it can be easier to do everything correctly through watching someone do it.
Hope this helps anyone else that has the same issue! It has been really helpful for me since I figured it out, before I had days where I couldn't get into shadow and did several full resets but always got the error again no matter what network I was on, settings I tried etc.
Alright, good luck to everyone and be well! -M