Which NRF24L01 modules are you using ? There are 2 main types. Those which come with an antenna and power amplifier (usually described as NRF24L01 + LNA + PA) and basic modules with just the main NRF24L01 chip. Provide a link to the supplier page.
Can you show a picture of your installation with the standard Uno and standard Nano on which you last did your tests ?
That it did not work at all with the setting radio.setPALevel(RF24_PA_LOW); sounds odd. Could you isolate that to the transmitter and did you try swapping the modules (you said you had 10)