I have a TP-Link C2600 and just tried upgrading to 18.06.2. All went well until I tried to access my router and I receive "invalid username and password". I have been using LEDE/OpenWRT for 4+ years now and I have never expereinced an upgrade problem like this.
I downgraded to 18.06.1 and attempted to restore my backup generated on 9 Jan '19, and again I receive invalid password / username. This is inspite of trying setting a password and not setting a password scenarios multiple time.
I'm not exactly sure what you mean. I have tried entering a new password, using my old password, and not entering a password when I upgrade. If there is an option in the backup to not restore the password, I don't know how to do that.
Unfortunately, the "shadow file" suggestion did not work. It was interesting though. When I entered the password I did not receive an "invalid username / password" message. The screen just popped back to the home screen. On other attempts, I always received the invalid username / password message.
I am at 18.06.1 now, and it works. I prefer not to have to rebuild my system: I rather restore settings but I guess I've got no choice at this point.
And yes, I did do a sysupgrade with the "keep settings" tick box checked.
There is something very strange happening with my system. My old network was 192.168.2.1. Of course the default is 192.168.1.1 for OpenWRT when installing new. Since I have been trying to reset everything and do a complete new install, I have not been successful changing the lan network to 192.168.2.1.
I am feeling pretty stupid at this point, really. I changed the lan interface and ensure it is set to static and still, when I reboot the router, and reload my nic, my IP is showing 192.168.1.102, even though the luci settings clearly have the lan set to 192.168.2.1, as a static address.
What to do?? Anyway, I will figure this out even if I have to go back to factory settings!!
ok, I am back in business!! I ssh'd and updated packages after reinstalling 18.06.2. I updated packages list, checked "list-upgradable, and id'd which ones needed updating. I basically reinstalled luci and now I'm good to go. Not sure which package was giving the problem logging on with luci, but it appears to be one of the luci libraries.
However as @lleachii stated, don't continue to upgrade packages, only re-install the missing packages otherwise you might end up in the same boat as in your first post!