It's likely an issue related to the modules' electric supply. The effects can be packet loss (even down to zero bps) or loss of communication with the module.
Two things have to be covered with the nRF modules for them to work:
- current draw (i.e. power),
- decoupling/filtering (i.e. bypass capacitors).
Since you don't mention specific devices, I'm assuming you refer to an 'antenna' module with SMA (or RP-SMA) connector.
The Nordic Semiconductor nRF24l01+ that is typically used in these modules has a maximum power consumption well below 100mW.
A module with power amplifier (PA) draws significantly more power than the nRF chip alone, the total power consumption will be larger than 100mW.
An Arduino can only supply power according to it's onboard regulator capabilities.
The Minis (and Micros) feature a smaller regulator that cannot drive both the Atmel AVR microcontroller and the PA.
- provide a separate 3.3V regulator for the nRF module(s),
- place a capacitor directly at the modules' connector's supply pins.