Abrupt change in fuel use

Hi there!

- 2009 Prius with 204k
- Averaging about 45mpg based on car’s calculations.
- Catalytic converter replaced with non OEM at dealership due to theft

I noticed 50.5 MPG on my way home tonight which seemed strange although it’s not the first time. The weirdest part is that the gas tank is below half already. Temp has been varying quite a bit but currently 36 degrees. I’ve only driven 89 miles. Typically I get over 300 miles per fill up. I don’t understand how the gas gauge could be so low while the mpg calculator actually went up.

I called dealership and they are saying cat converter replacement wouldn’t cause this and gas leak or failing oxygen censor would trip engine light warning. Any ideas?

I recently asked what’s included in 200k service and was told coolant change (plural?) which is expensive.

Thanks!