ecobee Smart Thermostat Premium not reading temperature correctly

I have an ecobee Smart Thermostat Premium I bought in November 2023 and it's not been reading the temperature accurately since date of purchase. It came with a smart sensor and that's normally accurate but the actual thermostat is all over the place and has gotten worse recently.

I bought a separate thermometer that I use to show me the real temperature and keep it near the thermostat. Last night, the thermostat said it was 70º but the smart sensor said it was 74º and my thermometer said it was 75º. I modified the thermostat to be +5º and it showed 75º and the AC kicked on. This morning, the thermostat is showing 72º, the smart sensor is showing 69º and the thermometer is showing 68º. So, I had to go in and change it to +1º instead. However, tonight it'll probably be off again by 3-6º.

I used to keep it at +5º and wouldn't have to mess with it too often. However, we had a really bad cold week in January where it was below freezing, and the thermostat was way off then and I've been having to mess with it daily since.

The thermostat is in the hallway which is in the dead center of the house. It's not on a wall that's facing the exterior. The old thermostat was in the same place and was always accurate. Is it possible the thermostat is defective? I was considering buying a pair of smart sensors to put in other rooms to help with the average but that's another $100 and I'm already $200 deep in this thermostat.

Open to any suggestions here on what I can do to make it better.