I just send some sats to a 3rd party address. My understanding is that the ‘change’ UTXO should be returned to my original address. However, what happened was that a new address was created and the change is being send there. I still have control over this new address, as I can see the right amount of BTC on my Trezor Suite. Yet, I am puzzled on why a new address is generated instead of sending the ‘change’ back to my original address.
Any feedbacks are much appreciated.
Hello and thanks for joining us on the forum 
Thanks for reaching out. Don’t worry, what you’re experiencing is normal behavior. In a transaction, any remaining balance after sending the desired amount to the recipient is sent to a newly generated change address in your wallet. This is done for privacy and security reasons: constantly reusing the same address would expose all your transaction history to an observer, and would make coin management inside your wallet very confusing.
Please read our article What is a change address for more details.
I hope this answers your question!
Thanks for clarifying!