[Barrow4491]

Honestly I don't see any logical reason for this to happen. The "problematic" unit is able to receive all types of data packets except the ones with Temperature / Humidity data, which are even sent more frequently than others that it is processing without problem.

Have you tried to play around with the location, of the "problematic" unit?
You can also try to remove the antenna, and in place of it try to use a tiny wire of around 17cm. Start with a 17cm wire and progressively make it shorter, 0.2cm at a  time. Always monitor the blink rate of the led.

Werk,
When I get a bit of spare time I will do as you suggest in more detail regarding antenna length; currently I have been trying several locations with the same result.
I am at a loss to work out what it may be but assume it is hardware related, maybe the recieve unit may be somehow marginal.
Regards
Jim