Sorry for the confusion, I'll try to explain better.

When buying an item from the market, I open the Design menu then choose a specific tab and look through the items. When I've found an item I want to purchase, I then tap the item which places it on my board with a green outline. I then tap the outlined item to complete the purchase.

You're saying your game goes blank so in the above scenario, at which point is it going blank? How far into the process can you get? Is it only when trying to buy a new item or does it also give you trouble if you're trying to place an item you already own from the menu onto your board? Is it for every category of item or just a specific group of items such as wallpapers or floor decos?

Regardless of the answer, this is something you'll likely have to contact the team about directly via Support Ticket. Isolating which step specifically is causing the issue will be very helpful when you file the report, though.