We've made a small update to the game to change how the menus work for Workshop maps in the game to significantly improve load times and performance when subscribed to hundreds or thousands of maps.
When first viewing the Workshop maps in the menu after this update there might be some additional hitching due to any cached thumbnail images being converted to a different format, but following that it should be much smoother.
If you're subscribed to over 1000 levels/packs on the Workshop you might have experienced several days where they were unplayable in the game last week. This was due to some changes made by Steam which we were able to bring to their attention and they quickly fixed the problem and it shouldn't be an issue again going forward.
This update is exclusively related to the performance of Workshop menus, but we'll have more updates and improvements coming next year.
Version 1.2.3