Some observation from my side that could or could not be connected to the latest issues with AMD and maybe even NVidia Grafics:
The preloaded course when the game starts is in Harvest theme (I think its little brook manor). When i then start a course to play, while its loading 1st i see is the full plot of the preloaded course. Similar to this is the behaviour when changing from windowed to fullscreen and back using alt+enter. Here too the 1st thing is that some old screen pops up and then is replaced by what was the current screen before alt+enter.
When grafics disruption starts later then it starts with some trees that flicker and it's allways the same trees, no matter where on the plot they are. Could be that all of the sudden it tries to pick the tree for the current course and display it as the one from harvest theme. As if its fliping back and forth between the courses them and harvest (the preloaded). Now the problem could be that there are trees then in either theme do not exist or that are too different, like tree in one, bush in another.
What is new since december update, is that at exactly that point (when it starts to flicker trees), the fps drop massively.
Now on the more speculative level this could mean that while running the game there are allways 2 pictures loaded in that GPU's memory and that dataaccess to this memory fails at a certain point. (Loading more then one picture and just flipping display is a comon trick to speed up grafics.) Could be that one of the 2 pictures is not properly and completely initialized or loaded and during game play contain uninitialized pointers that when adressed show RR (random rubbish). The workaround for this would be to make sure, that for all themes EXACTLY the same memory structure is loaded into the grafics memory. The fix would be to make sure is completely loaded and initializes every time. I'm not saying that any of this must be true, - my programmer experiencies are somewhat older -, but it might be worth to check and eventually lead to the detection of the bug even if it's completely elsewhere. Good luck guys.