I don't see anything in your code which would be producing the problem. If you switch receivers between the nano and the uno, does the problem follow the receiver?
The new receiver I'm using is of superheterodyne type, could that be the problem?
Those receivers are typically "better" and have more range. Are there any other transmitters in the area?
How are the three arduino's and their antennas arranged? Do things change if they are moved to a different arrangement?
Are both receiver arduinos printing at the same time, once per second? If this is too fast to see any difference, try increasing the delay between transmissions, to see if the reception on the two receivers is at the same time.