I agree that the problem is in the relay circuitry. The fact that you aren’t hearing a click means the relay either isn’t getting a control voltage to cause it to switch or it just isn’t responding when it does receive the control voltage.
Seeing that it used to work and now it stopped working, the problem is most likely a cold solder joint (I’m about 80% sure that this is the problem based on my experience helping people with this same type of issue). It’s very rare for relays to break and seeing that the other features of the microcontroller are working, that’s probably not the problem. It could be the transistors, but that would be much less likely than a solder joint going cold over time.
That’s all I can say for now.
Good luck!
-Brach