UPDATE (9/29): The patch went live on Steam and MAS.
We have an update coming out soon to fix issues for 10.11, here's what you need to do if you're using mods:
- Figure out what mods you have.
- Find out where you got them.
- Reinstall them after you update RCT.
Whenever RollerCoaster Tycoon 3: Platinum is updated on the Mac App Store, the update basically removes extraneous content (read: modded content) from the AppBundle. This results in that content missing from any saved game data from before the update.
Simply replacing the mod files will replace the missing content. That is, you just need to re-download and replace the mods used in the affected save to get your save working again.
The Gameagent.com blog below can assist you with accessing those mods again, in case you’re not exactly sure from where you originally got them.
We recommend keeping copies of downloaded mod files in a place where you can easily access them in case this happens with subsequent updates.
Also, please keep in mind that almost all modded content is made for the Windows PC version of the game by Windows PC players using Windows PC tools to create said content. Basically, there’s no guarantee that any particular modded content will work with the Mac App Store version of the game.