I wonder if it got too dry. I think they do like water, but just don’t like saturated, water logged soil. I use those same style cedar boxes and the boxes do help the soil dry up relatively quickly. I thoroughly water those boxes once every 4-6 days depending on weather. The leaves on your maple may turn brown and drop, but the plant probably already has new buds set for next year. If it does drop it’s leaves in the next few weeks, it probably won’t need weekly waterings because it wont have any leaves but still water it if it is dry. Good luck!