SP2019 Server Quick Launch Nav missing on Modern sites after Aug CU patch install

David Graham We have also been affected by this issue for months! I finally got fed up and did some sleuthing in the code. It seems that the sp-pages-assembly.js file got replaced by a newer version which is creating most of these issues. 

I will preface this by saying, always make backups before you try unverified solutions such as this one. I did such by copying the files I would be replacing in a backup directory, in the case that I need to revert back later. 

In this directory:

C:\Program Files\Common Files\microsoft shared\Web Server Extensions\16\TEMPLATE\LAYOUTS\Next\spclient

There are some layout folders. One labeled 'default' and one as 'en-us'.  'en-us' in the URL pointed me to that folder as holding the offending file. In the console, it kept saying 'cannot read property 'call' of undefined' stemming from this file:

https://river.nflibrary.ca/_layouts/15/next/spclient/en-us/sp-pages-assembly.js?uniqueId=madS1

So I replaced the sp-pages-assembly.js file in the 'en-us' folder with the older file in the 'defaults' folder. (After backing it up)

After this, the navigation came back. There are some things that still don't look right as labels aren't being updated from machine labels for example. but the navigation is back and we can edit modern pages again. 

You may also need to open a CMD as Admin and run IIS reset as well as doing a hard reload on the site to get the updates to appear as caching can keep you from seeing the changes until then. 

It seems that the navigation missing could be stemming from an issue with the publishing bar on modern sites as the navigation would appear again if I was in a list, that uses the modern layout but has a list bar instead of a publishing bar. 

It's not perfect, but it's at least usable again.