Grand Theft Auto Online – Identifying Vehicles in GTA V Online

I think what you're describing is where you replace one expensive car with another in your first garage. This means that your previous car's tracker would have been removed and it wouldn't have been available from your garage... If this is what you're experiencing you mightn't be able to get your car back.

The only way I know to solve this is to re-buy your car and store it in your other garage and to make sure that it is going to your other garage before you store it. Otherwise I cannot help. But that is my opinion.

As per my answer to this question, it is not possible to change the event settings, despite Rockstar Games saying:

you can customize your session to decide exactly which ones will happen – so you can play as much or as little of this new content as you like

Each player is only able to customise the events that they see, and participation in any event is always voluntary:

If you’d like to turn off Freemode Event notifications, you can choose to hide it using the Interaction Menu. Select the “Hide Options” feature, then choose “Events”. In this menu, you can choose to hide all Events, or just those you’d rather not see. You can always unhide Events in the same menu.

Events appear every 12 minutes, but note that some events (e.g. Hunt The Beast) require a minimum number of players.

To back all this up, you can check out the Rockstar Games GTA V FAQ (emphasis mine):

Freemode Events are launched every 12 minutes from the end of the last Event. On occasions where there are not enough available players in session to launch any Event, launching may take a little longer. Once more players have joined, the Events will continue to launch.

Freemode Events are set up to launch the full variety of Events, so Events do not usually repeat if they’ve been recently played in that session. Also, different Events require a different minimum number of players before they trigger -- Hunt the Beast requires a minimum of 10 players in session before it can be launched.

Freemode Events are available in private sessions; however, many Freemode Events require a minimum number of participants in order to begin. Time Trials are not available in private or solo sessions.