Hi there, same happens to me.
Playing on PC/Laptop WIN 8.1, 8GB RAM, already lowered my display and rendering rate but nothing.
Get on to the updated main menue - tried to start with logout save and former save;
Tried to start logged in and offline - and i'd started PC new. Before i've already played over 800 hours nearly without bigger probs.
Please - help, I badly want to pet my pet whilst sitting in a chair in my shroom-castle up in the oak tree.
I forgot to mention that my update was related from Steam with 2,7 GB but I got 2,9 GB.