Some parts need a little time to “bed-in” after being replaced.
Gear cable housing, to take one example, can stretch and settle into place after a little use, so the cable tension needs to be fine-tuned – you may hear the tell-tale clicking of the chain.
Similarly, new disc brake pads and rotors will only achieve full stopping power after some use.
Whatever the issue is, you are always welcome to bring your bike in for complimentary after-service fine-tuning check up.