ADR does not work properly

Hi all.

I am using LoRa server and have activated the ADR. after every successful transmission from my end device, the Spreading Factor resets to 7 which causes next transmission to be failed. Is this behavior considered as normal?
I expect that device receive the proper SF from server after transmission according to the RSSI received from the server side (based on the margin which we set). I set the margin in the interval of 5dB to 20dB but the same still happens.