The Sims 4 keeps producing the same issue ever since its launch in 2014 where Sims would not sit properly where they usually should. However this mod manages to fix those issues, including seating issues which occur at weddings, watching music performances and watching movies.
This mod comes in different variations but it’s the best solution to download the version which comes with all seating fixes. To install it extract the .zip file to Electronic Arts > The Sims 4 > Mods folder. Make sure you’ve enabled your Mods / CC in the game options!