Unable to access webgui after update

[Huecuva]

I'm running Jellyfin in a headless Debian VM. I noticed today that I was unable to access my Jellyfin webgui to watch any of my movies. To fix it I restored a proxmox backup of my VM to before the last Jellyfin update and was able to reach the webgui. I then tried to run updates and again lost access to the webgui. Upon doing some research I've learned that is known and (more or less) expected behaviour for this particular significant update 

Following the recommendations here, I made sure my library listed only 100 items in the webgui. I made sure I was running 10.10.7 before doing up the update and made sure that I had stopped the Jellyfin service. I then ran

Code:

sudo apt update && sudo apt upgrade jellyfin -y 

in order to upgrade Jellyfin alone and take care of other upgrades to the server afterwords. However, I am still unable to access the webgui. 

I understand from the link I posted above that it could take several hours to finish migrating my media database based on the fact that I have several TB of movies and TV shows. However, there is mentioned something called the Startup UI. I am unable to access this. If it's supposed to appear in place of the standard webgui while the server does its thing, it's not working. If not, I don't know how to access it and I can't find anywhere on the Jellyfin site where it indicates how to access the Startup UI other than it is "only accessible in your configured local networks". What does that even mean? If it's accessible on the LAN via the same IP address as the server, what port do I need to go to? Again, if it's the same as the standard webgui, then it's not working.

Can anyone tell me if this is working correctly and how to access the Startup UI or how to fix this issue if it's not?