Press this button to change the time base setting:
By default it’s set to Musical (that little note), which follows tempo changes. I have no idea what you did to make the other channels Linear.
Cubase IS quite easy to use, but you have to understand that there’s a point where things can’t be simplified without slowing down or removing functionality for power users, adding a million menu options that become pointless once you become more experienced like some DAWs do, or redesigning big portions of the interface and code which is something that they’re already working on.
In this case, something you did changed your other tracks to Linear time base, which doesn’t follow the tempo changes. Cubase is designed to make this very unlikely to happen by accident, so I really have no idea what you did. This has never happened to me in any recent version of Cubase. Make sure that you’re using the latest update for your version, just in case this was some obscure bug: