The chance of the microcontroller being defective is pretty small, especially since it displays messages on the LCD correctly. The pin you pointed to is the MISO pin, which is part of the SPI bus. The microcontroller communicates with the Ethernet controller and SD card through the SPI bus. So if that pin is unreliable, it can definitely cause problems. I can only think of two reasons where the controller gets stuck at the ‘Detecting uSD card’ message: either an incompatible SD card has been inserted, or the microcontroller is having difficulty communicating with the Ethernet controller. In either case, it seems crucial to figure out why the MISO pin is unreliable.

One thing I suggest you do is to use soldering iron to heat up that solder joint and let it reflow. Sometimes if the solder joint spreads too much onto its nearby traces it can cause shorting to those traces. Make sure the solder joint is not touching any nearby trace. Use a magnifying glass will definitely help.