I just did a different test, I looked at the source code of the mysensors project, and also noticed an error message when I was trying to send the message as if it can't be sent (!TSP:MSG:SEND)
I then decided to do a test and call transportSendWrite(0,msgTempDiff.setSensor(64).set(0.121, 3).setDestination(8)) instead of send() to see if I can force it to be routed through the node 0 (I understand this forces it to be routed trough the gateway), and this worked, I can now receive the message in the other node (ID 8 )
My assumption at this point is that the normal send method is not able to route the message properly to the destination node. I also think I shouldn't be calling transportSendWrite as it seems more like an internal method, but for now this is more for testing and troubleshooting the issue.
Overall, it still doesn't work using the normal send method and I wouldn't want to use that internal method since I am not too such of the implications of calling it directly and if I am assuming anything with node 0 being always able to route the message (and this internal method may stop working in future versions)