Your MCU board has a short on the 3.3v rail somewhere then.
Best way to try and find it would be to inject 3.3v onto that rail of the MCU board with a bench top PSU and see what gets hot first. Could just be a shorted Cap in there, could be a chip that's gone south. A thermal camera for that is great, but a Q-tip and rubbing alcohol will work just as well as it's going to evaporate much quicker off of anything in there that is getting warm.