One track designer issue occured when I was joining the final straight track piece to station on a 1200m wooden coaster. Can't recall the other, sorry, but I was only working on wooden coasters yesterday when it happened. After relaunching the game I couldn't load my old coaster because I hadn't saved the design yet, but I rebuilt it and saved that one without any further crashes. The completed coaster wouldn't have been absolutely identical but I was trying to make a specific design so it would have been pretty close.
Scenario issue happened in Mel's World, I'm in year 2 with 1185 guests and in the middle of building a wooden wild mouse coaster. If I load back into the scenario the game freezes after about five seconds, even if I pan away from the half-built coaster and close any windows. I can definitely reproduce this because it happens every time I load my save game. On my way to this point in year 2 it also happened once or twice, though I don't recall the exact circumstances of that. There would have been less rides but that's about all I can offer for that.
I'd previously completed Pokey Park before Mel's World, with no issues. Pokey Park was after the track designer crashes. Today have completed Evergreen Gardens with no consequential issues, although I did have a big stutter once.
Hope that's helpful.