NC 16.0.4 NCP v1.16.3 (Debian 10 VM and RaspberryPi)
Browsers: Firefox 69.0 and Brave 0.68.132 on Linux Mint 19.2
I noticed that bookmarks were returning to the default NC icon and following some experimenting can see that the themed icon is only available (or saved to a bookmark) after login.
This appears to be a change of behaviour from earlier versions.