Wear out problem with Heltec V2 original? Degration of modules after 2 years?

#1

I used the V2 modules for around 2 years.
Spread: beetween 9 and 11.
Power: LoRa.setTxPower(20,RF_PACONFIG_PASELECT_PABOOST);
Transmission around 4 transmissions an hour. More a cool envirionment around 4-15 C.
In the beginning everything was fine. After month the transmissions were degraded and at the end the transmissions were really bad. Sometimes the Lora Module initialisiation failed. Sometimes the system stucked in transmission.
I bought now new modules: The clones of the V2 heltec modules. Now with the same software and new modules everything is working fine. I reduced now the TX power to 17 to protect the modules. Is this necessary?
LoRa.setTxPower(17,RF_PACONFIG_PASELECT_PABOOST);

#2

Quite possibly the poor antennas supplied.