Software Updater is not working properly
Solution 1:
Firstly, update the following:
sudo apt autoremove && sudo apt autoclean -y
then open nano by sudo nano /etc/apt/sources.list
and check for any mismatches of default ubuntu update repo's:
Note -
16.04 - Xenial
18.04 - Bionic
deb http://in.archive.ubuntu.com/ubuntu/ bionic main restricted universe multiverse
deb http://in.archive.ubuntu.com/ubuntu/ bionic-updates main restricted universe multiverse
deb http://in.archive.ubuntu.com/ubuntu/ bionic-backports main restricted universe multiverse
deb http://security.ubuntu.com/ubuntu bionic-security main restricted universe multiverse
deb-src http://in.archive.ubuntu.com/ubuntu/ bionic main restricted universe multiverse
deb-src http://security.ubuntu.com/ubuntu bionic-security main restricted universe multiverse
deb-src http://in.archive.ubuntu.com/ubuntu/ bionic-backports main restricted universe multiverse
deb-src http://in.archive.ubuntu.com/ubuntu/ bionic-updates main restricted universe multiverse
If its easier then, delete the lines by pressing 'CTRL + K' in nano. and copy-paste them with the ones provided above to you.
Press 'CTRL + X', to exit. Prompts to save - Press 'Y' to save.
Type cat /etc/apt/sources.list
to double-check if they are correct.
Then do a sudo apt update && sudo apt upgrade -y
Hopefully should have fixed your issues after this.