This can be caused by a faulty repository.
As @anon6471198 suggested, please run sudo apt update and read the terminal output looking for any 404 errors or failed connections.
Once you identify which repository is failing to connect, remove the Repository either with the sudo add-apt-repository --remove command or by using software & Updates > Other tab.
You can check the net to see if the package you were using that repository for has a newer maintainer.
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