Considering your mileage (kilometerage?) is around 12.000, perhaps your total accumulated drive time has reached 100 hours, because the display can’t actually show 100 hours it resets back to 0 and in doing so resets your averages, defaulting back to a very optimistic range. Maybe check the page with total accumulated drive time to check that.
But you definitely also want to the calibration charge occasionally.
But if it's doing that, why the silly-optimistic range?
My SE gets its long charge regularly, and the stupidest range I've ever seen it admit to (twice) was about 230 miles. Both times it was on the Tesla chargers at Fort William, after frustratingly slow drives across Rannoch Moor and through Glen Coe, with rubbernecking tourist buses cluttering up the landscape. I suspect my fuel economy had been quite spectacular at that point.
It can be a bit of a fiddle to organise on the lowest tariff if you have a low overnight period, but I manage it with Octopus IG by refusing to let them start the charge till 11.30 when the cheap rate starts (it suits me not to start earlier), then asking for 100% by 7.30 am.
Come home below 10% if you have to do a wee detour to achieve that. If possible let the car sit for a couple of hours before starting the charge, to let it get a good look at the bottom of the well. Charge it (on AC, obviously) all the way to 100% in a single operation, and then let it do its balance charge. (Make sure there is enough time set on the charger to let it do that, once the charge has started.) And Bob's your uncle. Do it every few months at least.
The LFP battery has a very flat charging curve and it keeps track of where it is on the curve mainly by adding and subtracting charge and usage. But this will gradually accumulate errors over time. Imagine it like a well and you're trying to figure out how much water is in it by keeping track of water running in versus bucketloads taken out. Eventually you're a fair bit out. Then one day you take a lot out, and the car suddenly sees the bottom of the well, which it hadn't seen for a long time, and goes, oops, sorry, there's a fair bit less there than I thought. It recalculates hastily, and suddenly that 20 miles you thought you had is only five. Or less. You avoid this by letting it get a look at the bottom and then recording exactly how much it takes to get to the top, under controlled conditions, every so often.