After many months of correct communication between sensors equipped with Microchip RN2483 module from same days we experienced that new sensor added to TTN community correctly JOIN the network but, when transmitting data, the microrpocessor receives from RN2483 module the ok message but not the mac_tx_ok indicating the successful completion of the transmission.
Already registered sensors instead continue to communicate correctly. The problem is not present on alternative network servers (e.g. LORIOT)
This is a known issue with firmware 1.0.5 of the RN2483 modules in combination with TTN Stack. See the discussion at Excess LinkADRReq parameter bytes?
Thank You Kersing, the problem was exactly as you suggested. We have solved by initially setting ADR OFF and then enabling ADR after first transmission.