The first thing I've noticed is that now I can't connect to Internet anymore when I use VPN profile. If instead I'll restore the DUMBAP configuration, it works without issues.
I haven't got this issue when I updated from 19.07.3 to the .4 release.
User installed packages are not preserved after an upgrade, if they are not part of the OpenWrt image. You'll have to use opkgscript to restore them automatically, or create a custom image which includes the extra packages by default.