im trying to adopt cats. the event never started and the cats disappeared.

Could you please edit your post and fill out the bug form ? Seems you weren't prompted for it.

Editing should help with that.

If you still aren't prompted, please include this form + answers in your post

Product: The Sims 4
Platform:
Which language are you playing the game in? 
How often does the bug occur? 
What is your current game version number? 
What expansions, game packs, and stuff packs do you have installed? 
Steps: How can we find the bug ourselves? 
What happens when the bug occurs? 
What do you expect to see? 
Have you installed any customization with the game, e.g. Custom Content or Mods?
Did this issue appear after a specific patch or change you made to your system? 

Moving this to game issues for more troubleshooting/info