If you haven't changed anything about your driving style, I would suspect a difference in fuel formulation maybe. Just a guess. I could be in left field. Or perhaps you might have something going on ... like a caliper starting to sieze. I seriously doubt any change to your ECU program tripping over 100k.
Most of the year down south here, we have #2 diesel fuel. At some point, for a short time in the winter, we switch the #1. #1 has more anti-gel additives or some such crap. I'm not a fuel expert. #1 yields lower mpg that #2. Not a huge amount lower, but it is measurable.
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View my fuel log 2020 Mirage ES 1.2 manual: 42.4 mpg (US) ... 18.0 km/L ... 5.5 L/100 km ... 50.9 mpg (Imp)