Soldering 0.5 pitch components is a challenge to get right. My latest problem have been cold soldering. Meaning that pins look ok, but as I test them I have no connection. Not sure if this is lack of temperature, lack of solder tin or what, but I will have to find a more reliable way because it has caused a lot of issues lately.
The illustration above shows the problem. Pins look as if they are soldered, but in fact they are not. I suspect a combination of to little paste and to low temperatures, but lets see.
Having MCU’s you don’t trust don’t help, but just for the record the one I tested did work!